CVE-2026-11403: 
Sonatype Nexus 3 vulnerability analysis and mitigation

CVE-2026-11403 is an Insufficient Entropy vulnerability in Sonatype Nexus Repository Manager's format-specific API key generation that may allow a remote attacker to gain unauthorized access to repository operations as a targeted user. It affects all Sonatype Nexus Repository 3.x CE/Pro versions from 3.0.0 up to (but not including) 3.93.0, and was disclosed on July 14, 2026. The vulnerability carries a CVSS v4.0 base score of 8.7 (High) (Sonatype Advisory, Sonatype Release Notes).

The root cause is classified as CWE-331 (Insufficient Entropy), meaning the algorithm used to generate format-specific API keys (NuGet API Key, Docker Bearer Token, npm Bearer Token, and Conan) produces keys with insufficient randomness, making them predictable or recoverable by an attacker. Exploitation requires no authentication or user interaction — an attacker only needs to identify a valid Nexus username (which may be visible in repository asset metadata) and then derive or brute-force the corresponding API key. Three preconditions must all be met: a format-specific API key realm must be enabled on the instance, the targeted user must have an active API key, and the attacker must know or guess a valid username. This attack pattern maps to CAPEC-59 (Session Credential Falsification through Prediction) (Sonatype Advisory).

A successful attacker can authenticate to Nexus Repository as the targeted user using a recovered API key, potentially gaining unauthorized read access to all repositories that user can access, or unauthorized write access to hosted repositories if the targeted user has publish permissions. API keys are independent of user passwords and do not expire by default, meaning compromised keys remain valid until explicitly regenerated. The confidentiality impact is high, as sensitive packages, internal artifacts, and proprietary code stored in the repository could be exposed; integrity may also be affected if the targeted user has write permissions (Sonatype Advisory).

As of the advisory date (July 14, 2026), Sonatype is not aware of this vulnerability being exploited in the wild, and no public proof-of-concept exploit has been identified. The EPSS score is approximately 0.35%, indicating a low current probability of exploitation. The NVD SSVC assessment classifies exploitation as "none" and the attack as non-automatable. The vulnerability is not listed in the CISA Known Exploited Vulnerabilities (KEV) catalog (Sonatype Advisory).

1. Reconnaissance: Identify internet-facing Sonatype Nexus Repository Manager instances running versions 3.0.0 through 3.92.x using tools like Shodan or Censys, or by browsing to the Nexus web UI.
2. Username enumeration: Browse publicly accessible repository asset metadata or component information pages to identify valid usernames, which may be exposed in artifact upload history or component ownership fields.
3. Verify realm configuration: Confirm that a format-specific API key realm (NuGet API Key, Docker Bearer Token, or npm Bearer Token) is enabled on the target instance by attempting authentication against the relevant endpoint (e.g., NuGet feed, Docker registry, or npm registry URL).
4. Key prediction/recovery: Exploit the insufficient entropy in the API key generation algorithm to predict or brute-force the targeted user's format-specific API key, using knowledge of the flawed algorithm.
5. Authenticate as target user: Use the recovered API key to authenticate against the relevant format endpoint (e.g., NuGet feed, Docker registry, or npm registry) as the targeted user.
6. Perform unauthorized operations: Read sensitive packages from private repositories or, if the targeted user has write permissions, publish malicious or unauthorized packages to hosted repositories (Sonatype Advisory).

• Network: Unexpected or anomalous API authentication requests to NuGet, Docker, or npm endpoints from unfamiliar IP addresses; repeated authentication attempts against format-specific API endpoints suggesting key enumeration.
• Logs: Nexus Repository access logs showing successful API key-based authentication from IP addresses not associated with the legitimate user; access to repositories outside of normal business hours or from unusual geographic locations.
• Behavioral: Unexpected package downloads or uploads attributed to a user account from an IP address inconsistent with that user's normal activity; new packages published to hosted repositories by users who do not typically publish.

Sonatype recommends upgrading to Sonatype Nexus Repository Manager CE/Pro version 3.93.0 or later, which fixes the key generation algorithm. After upgrading, all users with active format-specific API keys (NuGet, Docker, npm, Conan) should regenerate their keys, as existing keys remain valid but were generated with the vulnerable algorithm. As an interim workaround if upgrading immediately is not possible, disable format-specific API key realms (NuGet API Key, Docker Bearer Token, npm Bearer Token) if they are not required for operations, and monitor repository access logs for suspicious activity (Sonatype Advisory, Sonatype Release Notes).

The vulnerability was discovered and responsibly reported by Sanjok Karki (@thesanjok) of National Forensic Sciences University, Goa, through Sonatype's Bug Bounty Program. Sonatype published a formal security advisory on July 14, 2026, proactively notifying customers through standard security advisory channels. No significant broader media coverage or notable community commentary beyond the official advisory has been identified at this time (Sonatype Advisory).