{"id":"EUVD-2026-19289","revision":null,"records":[{"revision":"d1df28b4e5444648aa9d0d2a482ae858","observedAt":"2026-10-23T15:48:27.903+00:00","statement":{"source":"cve-program","id":"CVE-2026-33540","aliases":[],"title":"Distribution affected by pull-through cache credential exfiltration via www-authenticate bearer realm","description":"Distribution is a toolkit to pack, ship, store, and deliver container content. Prior to 3.1.0, in pull-through cache mode, distribution discovers token auth endpoints by parsing WWW-Authenticate challenges returned by the configured upstream registry. The realm URL from a bearer challenge is used without validating that it matches the upstream registry host. As a result, an attacker-controlled upstream (or an attacker with MitM position to the upstream) can cause distribution to send the configured upstream credentials via basic auth to an attacker-controlled realm URL. 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Prior to 3.1.0, in pull-through cache mode, distribution discovers token auth endpoints by parsing WWW-Authenticate challenges returned by the configured upstrea…","description":"Distribution is a toolkit to pack, ship, store, and deliver container content. Prior to 3.1.0, in pull-through cache mode, distribution discovers token auth endpoints by parsing WWW-Authenticate challenges returned by the configured upstream registry. The realm URL from a bearer challenge is used without validating that it matches the upstream registry host. As a result, an attacker-controlled upstream (or an attacker with MitM position to the upstream) can cause distribution to send the configured upstream credentials via basic auth to an attacker-controlled realm URL. 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This vulnerability is fixed in 3.1.0.","state":0,"publishedAt":"2026-04-06T15:17:10.95+00:00","modifiedAt":"2026-06-17T10:37:40.78+00:00","affected":[],"metrics":[{"system":"CVSS 3.1 · security-advisories@github.com · Secondary","vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N","score":7.5,"severity":"HIGH"}],"references":["https://github.com/distribution/distribution/security/advisories/GHSA-3p65-76g6-3w7r"],"sourceUrl":"https://nvd.nist.gov/vuln/detail/CVE-2026-33540","license":"NIST NVD usage terms; underlying source attribution retained","enrichment":{"sourceStatus":"Analyzed","weaknesses":["CWE-918"],"productCriteria":["cpe:2.3:a:distribution_project:distribution:*:*:*:*:*:go:*:*"],"sourceDates":{"published":"2026-04-06T15:17:10.950","lastModified":"2026-06-17T10:37:40.780"},"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-2026-33540","identifiers":["CVE-2026-33540"]},"retained":false,"historicalAffected":[]},{"revision":"31c0916b0edf41acbb51cf5273c0dce7","observedAt":"2026-10-24T13:19:41.952+00:00","statement":{"source":"osv","id":"GHSA-3p65-76g6-3w7r","aliases":["CVE-2026-33540","GO-2026-5094"],"title":"Distribution affected by pull-through cache credential exfiltration via www-authenticate bearer realm","description":"hi guys,\n\ncommit: 40594bd98e6d6ed993b5c6021c93fdf96d2e5851 (as-of 2026-01-31)\ncontact: GitHub Security Advisory (https://github.com/distribution/distribution/security/advisories/new)\n\n## summary\n\nin pull-through cache mode, distribution discovers token auth endpoints by parsing `WWW-Authenticate` challenges returned by the configured upstream registry. the `realm` URL from a bearer challenge is used without validating that it matches the upstream registry host. as a result, an attacker-controlled upstream (or an attacker with MitM position to the upstream) can cause distribution to send the configured upstream credentials via basic auth to an attacker-controlled `realm` URL.\n\nthis is the same vulnerability class as CVE-2020-15157 (containerd), but in distribution’s pull-through cache proxy auth flow.\n\n## severity\n\nHIGH\n\nnote: the baseline impact is credential disclosure of the configured upstream credentials. if a deployment uses broader credentials for upstream auth (for example cloud iam credentials), the downstream impact can be higher; i am not claiming this as default for all deployments.\n\n## impact\n\ncredential exfiltration of the upstream authentication material configured for the pull-through cache.\n\nattacker starting positions that make this realistic:\n- supply chain / configuration: an operator configures a proxy cache to use an upstream that becomes attacker-controlled (compromised registry, stale domain, or a malicious mirror)\n- network: MitM on the upstream connection in environments where the upstream is reachable over insecure transport or a compromised network path\n\n## affected components\n\n- `registry/proxy/proxyauth.go:66-81` (`getAuthURLs`): extracts bearer `realm` from upstream `WWW-Authenticate` without validating destination\n- `internal/client/auth/session.go:485-510` (`fetchToken`): uses the realm URL directly for token fetch\n- `internal/client/auth/session.go:429-434` (`fetchTokenWithBasicAuth`): sends credentials via basic auth to the realm URL\n\n## reproduction\n\nattachment: `poc.zip` (local harness) with canonical and control runs.\n\nthe harness is local and does not contact a real registry: it uses two local HTTP servers (upstream + attacker token service) to demonstrate whether basic auth is sent to an attacker-chosen realm.\n\n```bash\nunzip -q -o poc.zip -d poc\ncd poc\nmake canonical\nmake control\n```\n\nexpected output (excerpt):\n\n```\n[CALLSITE_HIT]: getAuthURLs::configureAuth\n[PROOF_MARKER]: basic_auth_sent=true realm_host=127.0.0.1 account_param=user authorization_prefix=Basic\n```\n\ncontrol output (excerpt):\n\n```\n[CALLSITE_HIT]: getAuthURLs::configureAuth\n[NC_MARKER]: realm_validation=PASS basic_auth_sent=false\n```\n\n## suggested remediation\n\nvalidate that the token `realm` destination is within the intended trust boundary before associating credentials with it or sending any authentication to it. one conservative option is strict same-host binding: only accept a realm whose host matches the configured upstream host.\n\n## fix accepted when\n\n- distribution does not send configured upstream credentials to an attacker-chosen realm URL\n- a regression test covers the canonical and blocked cases\n\n[addendum.md](https://github.com/user-attachments/files/24984637/addendum.md)\n[poc.zip](https://github.com/user-attachments/files/24984638/poc.zip)\n[PR_DESCRIPTION.md](https://github.com/user-attachments/files/24984639/PR_DESCRIPTION.md)\n[RUNNABLE_POC.md](https://github.com/user-attachments/files/24984640/RUNNABLE_POC.md)\n\n\nbest,\noleh","state":0,"publishedAt":"2026-04-06T17:52:52+00:00","modifiedAt":"2026-09-10T03:50:42.4263125+00:00","affected":[{"ecosystem":"Go","name":"github.com/distribution/distribution/v3","ranges":[{"type":"SEMVER","events":[{"kind":"introduced","version":"0"},{"kind":"fixed","version":"3.1.0"}]}],"versions":[],"rawVersionEvidence":null},{"ecosystem":"Go","name":"github.com/distribution/distribution","ranges":[{"type":"SEMVER","events":[{"kind":"introduced","version":"0"},{"kind":"last_affected","version":"2.8.3"}]}],"versions":[],"rawVersionEvidence":null}],"metrics":[{"system":"CVSS_V3","vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N","score":null,"severity":null},{"system":"Publisher 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