CVE-2025-9868: Sonatype Nexus Repository SSRF Vulnerability

CVE-2025-9868 Overview

CVE-2025-9868 is a Server-Side Request Forgery (SSRF) vulnerability in the Remote Browser Plugin of Sonatype Nexus Repository 2.x, affecting versions up to and including 2.15.2. The flaw allows unauthenticated remote attackers to issue crafted HTTP requests that coerce the Nexus server into making outbound requests on the attacker's behalf. Successful exploitation enables exfiltration of proxy repository credentials stored within the Nexus instance. The vulnerability is classified under CWE-918: Server-Side Request Forgery.

Critical Impact

Unauthenticated remote attackers can exfiltrate proxy repository credentials from affected Sonatype Nexus Repository 2 instances through crafted HTTP requests to the Remote Browser Plugin.

Affected Products

• Sonatype Nexus Repository 2.x (all versions through 2.15.2)
• Remote Browser Plugin component in Nexus Repository 2
• Proxy repository configurations holding upstream credentials

Discovery Timeline

• 2025-10-08 - CVE-2025-9868 published to NVD
• 2026-04-15 - Last updated in NVD database

Technical Details for CVE-2025-9868

Vulnerability Analysis

The Remote Browser Plugin in Sonatype Nexus Repository 2 accepts HTTP requests that direct the server to fetch content from attacker-controlled URLs. Because the plugin does not adequately validate or restrict request targets, an unauthenticated attacker can send crafted requests that cause the server to issue outbound HTTP connections.

When the Nexus server processes these requests, it attaches credentials associated with configured proxy repositories. The attacker receives these credentials by directing the request to a server they control. This converts a server-side request forgery primitive into a credential exfiltration channel.

The exposure scope includes credentials for any upstream repository proxied through the Nexus instance. These credentials frequently grant access to private package registries, artifact stores, and partner repositories, expanding the attack surface beyond the Nexus instance itself.

Root Cause

The vulnerability stems from missing access control and missing URL validation in the Remote Browser Plugin. The plugin processes requests without authentication and without restricting destination hosts or schemes. It also reuses configured proxy repository credentials when generating outbound requests, allowing those credentials to be sent to attacker-chosen endpoints.

Attack Vector

The attack is network-based, requires no privileges, and requires no user interaction. An attacker identifies an exposed Nexus Repository 2 instance, sends an HTTP request to the Remote Browser Plugin endpoint specifying an attacker-controlled URL, and captures the inbound request on their server. The captured request contains the proxy repository credentials in the Authorization header or equivalent credential fields. Refer to the Sonatype Support Article for vendor-supplied technical details.

Detection Methods for CVE-2025-9868

Indicators of Compromise

• Outbound HTTP or HTTPS connections from the Nexus Repository server to unfamiliar external hosts, particularly to IP addresses outside configured proxy repository destinations
• Requests to the Remote Browser Plugin endpoint originating from untrusted source IPs in Nexus access logs
• Unexpected authentication failures or anomalous logins on upstream repositories whose credentials are stored in Nexus
• Outbound traffic from Nexus that does not correlate with scheduled artifact fetch or proxy operations

Detection Strategies

• Inspect Nexus request.log and nexus.log files for Remote Browser Plugin invocations referencing external URLs
• Correlate outbound network flows from the Nexus host against the list of configured proxy repository targets and flag deviations
• Deploy web application firewall rules that block unauthenticated requests to Remote Browser Plugin paths
• Monitor upstream repository providers for credential reuse from unexpected source IPs

Monitoring Recommendations

• Enable verbose access logging on the Nexus Repository server and forward logs to a centralized analytics platform
• Alert on any outbound connection from the Nexus host to non-allowlisted destinations
• Track failed and successful authentication events on every proxied upstream repository
• Review proxy repository credential usage on a recurring schedule for anomalous geographic or temporal patterns

How to Mitigate CVE-2025-9868

Immediate Actions Required

• Restrict network access to Nexus Repository 2 administrative and plugin endpoints using firewall or reverse-proxy access control lists
• Rotate all proxy repository credentials configured in affected Nexus instances, as they may already be exposed
• Disable the Remote Browser Plugin if it is not required for business operations
• Audit Nexus access logs for prior exploitation attempts targeting the Remote Browser Plugin

Patch Information

Sonatype Nexus Repository 2 reached end-of-life status, and organizations should consult the Sonatype Support Article for vendor remediation guidance. Migration to Nexus Repository 3, which is unaffected by this issue, is the recommended long-term path.

Workarounds

• Place Nexus Repository 2 behind an authenticating reverse proxy that blocks unauthenticated requests to plugin endpoints
• Use network segmentation to prevent the Nexus host from initiating outbound connections to arbitrary destinations
• Configure egress filtering that allowlists only the hostnames of legitimate upstream repositories
• Remove stored proxy credentials for upstream repositories that support unauthenticated read access

# Example egress allowlist using iptables to restrict Nexus outbound traffic
# Replace ALLOWED_HOST entries with your legitimate upstream repository hosts
iptables -A OUTPUT -o eth0 -d repo.maven.apache.org -j ACCEPT
iptables -A OUTPUT -o eth0 -d registry.npmjs.org -j ACCEPT
iptables -A OUTPUT -o eth0 -p tcp --dport 443 -j REJECT
iptables -A OUTPUT -o eth0 -p tcp --dport 80 -j REJECT