{"id":"CVE-2026-109584","revision":"3b911f90846d4303af08b27fc4a2f98a","records":[{"revision":"3b911f90846d4303af08b27fc4a2f98a","observedAt":"2026-10-26T15:35:30.984+00:00","statement":{"source":"cve-program","id":"CVE-2026-109584","aliases":[],"title":"HTTP/2 cookie crumb join expands a small HPACK header block into an unbounded allocation in Bandit","description":"Improper Handling of Highly Compressed Data (Data Amplification) vulnerability in the HTTP/2 implementation of mtrudel bandit allows an unauthenticated remote attacker to exhaust server memory via a small HPACK-compressed HEADERS block. The block stores one large cookie value in the HPACK dynamic table and then references it tens of thousands of times with 1-byte indexed fields. In the reporter's run, a 49 KB block made a server with default settings allocate a 183 MB cookie binary before any application code ran, and every concurrent stream can repeat the cost.\n\nBandit.HTTP2.Connection caps only the compressed block (max_header_block_size), and its check of the decoded list against max_header_list_size never fires because that setting defaults to :infinity. combine_cookie_crumbs/1 in lib/bandit/http2/stream.ex then joins every crumb into one binary.\n\nThis issue affects bandit: from 0.3.3 before 1.14.0.","state":0,"publishedAt":"2026-10-26T13:32:22.359+00:00","modifiedAt":"2026-10-26T13:32:22.359+00:00","affected":[{"ecosystem":"https://repo.hex.pm","name":"bandit","ranges":[],"versions":[],"rawVersionEvidence":"{\n                    \"collectionURL\": \"https://repo.hex.pm\",\n                    \"cpes\": [\n                        \"cpe:2.3:a:mtrudel:bandit:*:*:*:*:*:*:*:*\"\n                    ],\n                    \"defaultStatus\": \"unaffected\",\n                    \"packageName\": \"bandit\",\n                    \"packageURL\": \"pkg:hex/bandit\",\n                    \"product\": \"bandit\",\n                    \"repo\": \"https://github.com/mtrudel/bandit\",\n                    \"vendor\": \"mtrudel\",\n                    \"versions\": [\n                        {\n                            \"lessThan\": \"1.14.0\",\n                            \"status\": \"affected\",\n                            \"version\": \"0.3.3\",\n                            \"versionType\": \"semver\"\n                        }\n                    ]\n                }"},{"ecosystem":"https://github.com","name":"mtrudel/bandit","ranges":[],"versions":[],"rawVersionEvidence":"{\n                    \"collectionURL\": \"https://github.com\",\n                    \"cpes\": [\n                        \"cpe:2.3:a:mtrudel:bandit:*:*:*:*:*:*:*:*\"\n                    ],\n                    \"defaultStatus\": \"unaffected\",\n                    \"packageName\": \"mtrudel/bandit\",\n                    \"packageURL\": \"pkg:github/mtrudel/bandit\",\n                    \"product\": \"bandit\",\n                    \"repo\": \"https://github.com/mtrudel/bandit\",\n                    \"vendor\": \"mtrudel\",\n                    \"versions\": [\n                        {\n                            \"lessThan\": \"220b9dfd27f9a21305be2afc75cbe585ddc24e7a\",\n                            \"status\": \"affected\",\n                            \"version\": \"44bf969cd59851622fb6ee4d16227fbc39a77fb4\",\n                            \"versionType\": \"git\"\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:N/VA:H/SC:N/SI:N/SA:N","score":8.7,"severity":"HIGH"}],"references":["https://github.com/mtrudel/bandit/security/advisories/GHSA-7gfj-7gvq-3xqj","https://cna.erlef.org/cves/CVE-2026-109584.html","https://osv.dev/vulnerability/EEF-CVE-2026-109584","https://github.com/mtrudel/bandit/commit/44bf969cd59851622fb6ee4d16227fbc39a77fb4","https://github.com/mtrudel/bandit/commit/220b9dfd27f9a21305be2afc75cbe585ddc24e7a"],"sourceUrl":"https://www.cve.org/CVERecord?id=CVE-2026-109584","license":"CVE Program Terms of Use","key":"cve-program:CVE-2026-109584","identifiers":["CVE-2026-109584"]},"retained":false,"historicalAffected":[]}],"coverage":[]}