CVE-2026-8034: github enterprise_server Interpretation Conflict

Vulnerability summary

CVE-2026-8034 is a critical (CVSS 9.8) Interpretation Conflict vulnerability in github enterprise_server. EPSS estimates a 0.86% chance of exploitation in the next 30 days, higher than 57.7% of scored vulnerabilities.

Timeline

1. 07-05-2026
   PublishedVulnerability first disclosed.
2. 08-05-2026
   Last modifiedVulnerability information updated.

Description

A server-side request forgery (SSRF) vulnerability was identified in the GitHub Enterprise Server notebook viewer that allowed an attacker to access internal services by exploiting URL parser confusion between the validation layer and the HTTP request library. The hostname validation used a different URL parser than the request library, enabling a crafted URL to pass validation while directing the request to an unintended host. Exploitation required network access to the GitHub Enterprise Server instance. This vulnerability affected all versions of GitHub Enterprise Server prior to 3.21 and was fixed in versions 3.16.18, 3.17.15, 3.18.9, 3.19.6, and 3.20.2. This vulnerability was reported via the GitHub Bug Bounty program.

• CWE-436Interpretation ConflictProduct A handles inputs or steps differently than Product B, which causes A to perform incorrect actions based on its perception of B's state.
• CWE-918Server-Side Request Forgery (SSRF)The web server receives a URL or similar request from an upstream component and retrieves the contents of this URL, but it does not sufficiently ensure that the request is being sent to the expected destination.