SSRF in Distribution
CVE-2026-33540
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. This vulnerability is fixed in 3.1.0.
Vulnerability class: SSRF (Server-Side Request Forgery)
EPSS: 0.003 (19.6th percentile) — read the EPSS interpretation.
CVSS v3 metric
CVSS v3 base score 7.5 (High). Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N.
Affected products
- Distribution — versions < 3.1.0
- Distribution_project Distribution
Weakness classification (CWE)
References
- security-advisories@github.com (x_refsource_CONFIRM, Exploit, Mitigation, Vendor Advisory)
Frequently asked questions
- What is CVE-2026-33540?
- CVE-2026-33540 is a high-severity vulnerability in Distribution, classified under Server-Side Request Forgery (SSRF). CVSS score: 7.5/10. Published 2026-04-06.
- How severe is CVE-2026-33540?
- High severity. CVSS v3 base score is 7.5 out of 10.