Distribution affected by pull-through cache credential exfiltration via www-authenticate bearer realm

Exploitation

No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.

CVSS

7.5 · CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N

EPSS

• CVE-2026-33540: 0.29% estimated exploitation activity in the next 30 days; percentile 21.08 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.

As published by the source; long descriptions are shortened.

hi guys, commit: 40594bd98e6d6ed993b5c6021c93fdf96d2e5851 (as-of 2026-01-31) contact: GitHub Security Advisory (https://github.com/distribution/distribution/security/advisories/new) summary 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. this is the same vulnerability class as CVE-2020-15157 (containerd), but in distribution’s pull-through cache proxy auth flow. severity HIGH note: the baseline impact is credential disclosure of the configured upstream credentials. if a deployment uses broader credentials for upstream auth (for example cloud iam…

Published by the source

6 Apr 2026, 17:52 UTC

Last modified by the source

6 Apr 2026, 23:42 UTC

Source last checked

26 Oct 2026, 15:19 UTC

1. Revision 1 · created · 26 Oct 2026

   Published from ghsa record GHSA-3p65-76g6-3w7r

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# Patch Next advisory brief: CVE-2026-33540

Advisory: Distribution affected by pull-through cache credential exfiltration via www-authenticate bearer realm
IDs: CVE-2026-33540, GHSA-3p65-76g6-3w7r
Record: https://patchnext.com/advisories/cve-2026-33540 (revision 1, source checked 26 Oct 2026, 15:19 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: High (CVSS 7.5)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Partial vendor fix; fixed versions by package: github.com/distribution/distribution/v3 3.1.0. A vendor fix does not mean a deployment is fixed.

## Affected components
- Go github.com/distribution/distribution: affected <= 2.8.3
- Go github.com/distribution/distribution/v3: affected < 3.1.0; fixed in 3.1.0

## Suggested inspection (read-only)
- Go github.com/distribution/distribution: check the installed version with your package manager.
- Go github.com/distribution/distribution/v3: check the installed version with your package manager.

## Supported action
No complete vendor fix is recorded. Follow the primary source's mitigation guidance and check this record again before closing anything.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on github.com/distribution/distribution, github.com/distribution/distribution/v3.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://github.com/advisories/GHSA-3p65-76g6-3w7r (GitHub-reviewed advisory GHSA-3p65-76g6-3w7r lists affected ranges: Go github.com/distribution/distribution/v3 >=0 =0 <=2.8.3)

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