CVE-2026-8034: Server-side request forgery vulnerability in GitHub Enterprise Server notebook viewer via URL parser confusion
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.
Affected Software
Remediation
Recommended actions to resolve this vulnerability, in priority order.
- Upgrade
Upgrade to a fixed release to a version that resolves this vulnerability.
Fixed in 3.16.18 - Upgrade
Upgrade to a fixed release to a version that resolves this vulnerability.
Fixed in 3.17.15 - Upgrade
Upgrade to a fixed release to a version that resolves this vulnerability.
Fixed in 3.18.9 - Upgrade
Upgrade to a fixed release to a version that resolves this vulnerability.
Fixed in 3.19.6 - Upgrade
Upgrade to a fixed release to a version that resolves this vulnerability.
Fixed in 3.20.2
Event History
Frequently Asked Questions
What is the severity of CVE-2026-8034?
CVE-2026-8034 has been classified as a critical severity security vulnerability.
How do I fix CVE-2026-8034?
To mitigate CVE-2026-8034, update GitHub Enterprise Server to version 3.21 or later.
What are the potential impacts of CVE-2026-8034?
The potential impacts of CVE-2026-8034 include unauthorized access to internal services and data leakage.
Which versions of GitHub Enterprise Server are affected by CVE-2026-8034?
CVE-2026-8034 affects GitHub Enterprise Server versions prior to 3.21.
Is CVE-2026-8034 exploitable remotely?
Yes, CVE-2026-8034 can be exploited remotely by an attacker with access to the notebook viewer functionality.