CVE-2026-11403: Nexus Repository Auth Bypass Vulnerability

CVE-2026-11403 Overview

CVE-2026-11403 is a high-severity vulnerability in Sonatype Nexus Repository Manager affecting format-specific API key generation. A remote unauthenticated attacker can gain unauthorized access to repository operations while impersonating a targeted user. The flaw is exploitable only when a format-specific API key realm is enabled and the targeted user has an active API key. Affected realms include the NuGet API Key, Docker Bearer Token, and npm Bearer Token realms. The weakness is categorized under [CWE-331] (Insufficient Entropy), indicating predictable or guessable key material. Sonatype addressed the issue in Nexus Repository 3.93.0.

Critical Impact
A remote attacker can perform repository operations as another user without authentication, enabling package tampering and supply chain compromise across NuGet, Docker, and npm ecosystems.

Affected Products

Sonatype Nexus Repository Manager (versions prior to 3.93.0)
Deployments with NuGet API Key, Docker Bearer Token, or npm Bearer Token realms enabled
Users with active format-specific API keys

Discovery Timeline

2026-07-14 - CVE-2026-11403 published to NVD
2026-07-15 - Last updated in NVD database

Technical Details for CVE-2026-11403

Vulnerability Analysis

The vulnerability resides in how Sonatype Nexus Repository Manager generates format-specific API keys for the NuGet, Docker, and npm realms. The generation routine produces keys with insufficient entropy, allowing an attacker to predict or reproduce API key material tied to a targeted user. Once the attacker derives a valid key, the server accepts it as legitimate authentication for the associated user identity.

Because the affected realms authenticate package publishing and retrieval workflows, successful exploitation grants full repository operation privileges as the targeted account. This includes publishing malicious package versions, overwriting artifacts, and downloading private packages. The Sonatype Nexus Release Notes confirm the fix in version 3.93.0.

Root Cause

The root cause is [CWE-331] Insufficient Entropy in the format-specific API key generation logic. The keys are derived using a process that lacks sufficient randomness, making them predictable to an attacker with knowledge of the algorithm or observable inputs. Standard user-based API keys are not affected — only the NuGet, Docker, and npm bearer token realms exhibit the flaw.

Attack Vector

The attack requires network access to the Nexus Repository Manager instance and no prior authentication or user interaction. The attacker must know or enumerate a target username that has an active format-specific API key. After deriving the predictable key, the attacker submits authenticated API requests as the victim. See the Sonatype Support Article for vendor-provided context.

No public proof-of-concept has been released. The vulnerability is not listed in the CISA Known Exploited Vulnerabilities catalog. The EPSS probability is 0.349%.

Detection Methods for CVE-2026-11403

Indicators of Compromise

Unexpected package publishing events attributed to legitimate user accounts in NuGet, Docker, or npm repositories.
API requests using bearer tokens originating from unfamiliar IP addresses or geographies.
Newly published or overwritten package versions not correlated with CI/CD pipeline activity.
Authentication events for format-specific realms from outside expected build infrastructure ranges.

Detection Strategies

Audit Nexus Repository access logs for API key authentication events tied to the NuGet, Docker, and npm realms.
Correlate package publish timestamps with authorized developer activity and CI/CD build records.
Flag any API key reuse across disparate source IP addresses within short time windows.
Compare artifact checksums against expected build outputs to identify tampered packages.

Monitoring Recommendations

Forward Nexus Repository audit logs to a centralized SIEM for continuous review of authentication and publish events.
Alert on any use of format-specific API keys outside approved network ranges or build agents.
Track new package versions and artifact overwrites, requiring approval workflows for high-value repositories.

How to Mitigate CVE-2026-11403

Immediate Actions Required

Upgrade Sonatype Nexus Repository Manager to version 3.93.0 or later immediately.
Rotate all active NuGet, Docker, and npm API keys after upgrading to invalidate any predictable tokens.
Review recent repository publish and download activity for unauthorized operations.
Notify users with active format-specific API keys to regenerate credentials.

Patch Information

Sonatype released the fix in Nexus Repository 3.93.0. Details are available in the Sonatype Nexus Release Notes and the Sonatype Support Article. Administrators should apply the patch before rotating credentials to ensure new keys are generated with sufficient entropy.

Workarounds

Disable the NuGet API Key, Docker Bearer Token, and npm Bearer Token realms if they are not required for operations.
Restrict network access to the Nexus Repository Manager administrative and API endpoints using firewall rules or a reverse proxy.
Require additional authentication controls such as mutual TLS or IP allowlisting for CI/CD integrations until patching is complete.

bash

# Configuration example - disable unused format-specific API key realms
# in Nexus Repository Manager Administration > Security > Realms
# Remove the following from Active Realms if not in use:
#   - NuGet API-Key Realm
#   - Docker Bearer Token Realm
#   - npm Bearer Token Realm