Raw vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:NCVSS and EPSS are reproduced from their sources (NVD, FIRST EPSS). Risk Priority is our own derived reading, not an NVD score.
Summary
CVE-2026-33540 is a high-severity SSRF (CWE-918) vulnerability in Distribution Project Distribution. Its CVSS base score is 7.5 (High).
Operationally, exploitation aligns with the MITRE ATT&CK technique Exploit Public-Facing Application (T1190); ranked at the 32th percentile by exploit likelihood (below the median); it is not currently listed in the CISA KEV catalog; a public proof-of-concept is referenced.
The strongest mitigations our analysis identified map to AC-4 (Information Flow Enforcement) and SI-10 (Information Input Validation) — see the control section below for these in your framework.
Deeper analysis AI-assisted summary
Synthesised by an AI model from the NVD description and linked references — a reading aid, not an authoritative source.
CVE-2026-33540 affects the Distribution toolkit, an open-source project used to pack, ship, store, and deliver container content, specifically versions prior to 3.1.0. In pull-through cache mode, Distribution discovers token authentication endpoints by parsing WWW-Authenticate challenges from the configured upstream registry. However, it uses the realm URL extracted from a bearer challenge without validating that it matches the upstream registry host, enabling potential credential leakage.
An attacker who controls the upstream registry or holds a man-in-the-middle (MitM) position to it can exploit this vulnerability. By crafting a malicious WWW-Authenticate challenge, the attacker can trick Distribution into sending the configured upstream credentials via basic authentication to an attacker-controlled realm URL. This results in high confidentiality impact (CVSS 7.5: AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N), classified under CWE-918 (Server-Side Request Forgery), allowing remote, unauthenticated attackers to steal credentials without requiring user interaction.
The GitHub security advisory (GHSA-3p65-76g6-3w7r) confirms the issue is fixed in Distribution version 3.1.0, recommending an upgrade to mitigate the vulnerability. No additional workarounds are specified in the provided references.
OWASP Top 10 for Web (2025)
EU & UK References
- 🇪🇺 ENISA EUVD: EUVD-2026-19289
Vulnerability Data
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…
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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.
- CWE(s)
Related Threats
MITRE ATT&CK Enterprise Techniques
CVEs Like This One
Affected Assets
Mitigating Controls
Control response
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V1.3.6V1.5.3V5.3.2V10.4.7
Mitigating Controls (NIST 800-53 r5) AI
Information flow enforcement can restrict which destinations the server is allowed to contact on behalf of users.
Input validation directly stops untrusted URLs from being accepted and fetched without destination checks.
Boundary protection limits the network reach of server-initiated requests even if SSRF occurs.
Mitigating Controls (NIST CSF 2.0) AI
Derived directly from the weakness types (CWEs) cited in the NVD entry via our AI-authored CWE→CSF cross-walk (authority under review) — links open the control.
Secure development practices directly include input validation and destination allow-listing that prevent SSRF.
Runtime monitoring of web applications and services can detect anomalous outbound requests indicative of SSRF.
Vulnerability identification processes can discover and record SSRF flaws in web applications.
Network segmentation and egress controls can limit the damage from successful SSRF requests.