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CVE-2026-11403 – Authentication Bypass via Weak API Key Generation – Sonatype Nexus Repository Ma…

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Summary

CVE-2026-11403 is a high-severity authentication bypass vulnerability in Sonatype Nexus Repository Manager’s format-specific API key generation mechanism, assigned a CVSS 4.0 score of 8.7. A flaw in the way the product generated API keys for NuGet, Docker Bearer Token, and npm Bearer Token authentication realms allowed a remote, unauthenticated attacker to gain unauthorized access to repository operations as a targeted user. Sonatype addressed this vulnerability in version 3.94.0, released July 9, 2026, by switching to UUID v4-based key generation for all affected formats.

Technical details

  • Root cause: Prior to version 3.94.0, Nexus Repository Manager generated format-specific API keys using a mechanism that lacked sufficient randomness. Sonatype’s 3.94.0 release notes confirm the fix, stating that the product "now generates API keys for NuGet, npm, Docker, and Conan formats using UUID v4," which "improves the randomness and uniqueness of generated keys, strengthening the overall security of authentication workflows." This indicates that keys generated by earlier versions were weak or predictable, enabling an attacker to forge or brute-force a valid key.
  • Trigger conditions: The vulnerability is exploitable only when at least one format-specific API key realm — NuGet API Key, Docker Bearer Token, or npm Bearer Token — is enabled in the Nexus security configuration, and the targeted user has an active API key issued under that realm.
  • Attack vector: Fully remote and unauthenticated. The CVSS 4.0 vector (AV:N/AC:L/AT:N/PR:N/UI:N) confirms no privileges or user interaction are required, and no special attack conditions apply beyond the realm and key prerequisites described above.
  • Impact: An attacker who successfully predicts or forges a valid format-specific API key can authenticate as a targeted user and perform repository operations on their behalf, gaining unauthorized read access to private packages and artifacts — including any credentials or sensitive data embedded within them (VC:H in CVSS 4.0). No integrity or availability impact is indicated by the CVSS vector.

Affected software

  • Sonatype Nexus Repository Manager 3.x, all versions prior to 3.94.0, where one or more of the following realms are enabled: NuGet API Key, Docker Bearer Token, or npm Bearer Token.

Severity

CVSS 4.0 base score: 8.7
Vector: CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:N/VA:N/SC:N/SI:N/SA:N

Mitigation and recommended actions

  • Immediate — upgrade: Upgrade Sonatype Nexus Repository Manager to version 3.94.0 or later, which resolves the vulnerability by generating format-specific API keys using UUID v4.
  • Post-upgrade — key rotation: After upgrading, regenerate all existing format-specific API keys (NuGet, Docker Bearer Token, and npm Bearer Token) for all users. Keys issued prior to 3.94.0 were generated under the weaker algorithm and should be considered potentially compromised. Sonatype recommends this step in its 3.94.0 release notes.
  • If immediate patching is not feasible: Disable the NuGet API Key, Docker Bearer Token, and npm Bearer Token realms in the Nexus Security → Realms configuration until patching can be completed. Additionally, restrict network-level access to Nexus Repository Manager instances to trusted internal networks or VPN only, reducing the attack surface for unauthenticated remote actors.

IONIX Status

The IONIX research team is tracking ongoing exploitation attempts and recommends immediate patching. Potentially affected assets are outlined in this post.

References

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