CVE-2026-8034

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.

CVSS v3.1 Score

9.8

CRITICAL

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

EPSS — Exploit Prediction

0.0006

Probability of exploitation

0.19%

Percentile rank

EPSS estimates the probability that this vulnerability will be exploited in the wild within the next 30 days. A higher score means more likely to be exploited.

Weakness Type (CWE)

CWE-436 CWE-436

CWE-918 Server-Side Request Forgery (SSRF)

Affected Products

Vendor	Product	Versions
github	enterprise_server	< 3.16.18
github	enterprise_server	3.17.0 — 3.17.15
github	enterprise_server	3.18.0 — 3.18.9
github	enterprise_server	3.19.0 — 3.19.6
github	enterprise_server	3.20.0 — 3.20.2

References

Advisories & Patches

https://docs.github.com/en/[email protected]/admin/release-notes#3.16.18 https://docs.github.com/en/[email protected]/admin/release-notes#3.17.15 https://docs.github.com/en/[email protected]/admin/release-notes#3.18.9 https://docs.github.com/en/[email protected]/admin/release-notes#3.19.6 https://docs.github.com/en/[email protected]/admin/release-notes#3.20.2

Frequently Asked Questions

What is CVE-2026-8034? +

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. It has a CVSS v3.1 base score of 9.8 (CRITICAL).

How severe is CVE-2026-8034? +

CVE-2026-8034 has a CVSS v3.1 score of 9.8 out of 10, rated CRITICAL. This is a critical vulnerability that should be patched immediately. The EPSS score is 0.0006, placing it in the 0th percentile for exploitation probability.

What products are affected by CVE-2026-8034? +

CVE-2026-8034 affects products from github, specifically: enterprise_server. Check the affected products table above for specific version ranges.

How do I check if I'm vulnerable to CVE-2026-8034? +

You can use Secably's free Website Scanner to check your website for known vulnerabilities. For infrastructure scanning, use the Port Scanner to identify exposed services that may be affected. Check the vendor advisories linked above for specific patch and version information.

Related Vulnerabilities

CVE-2025-54368

uv is a Python package and project manager written in Rust. In versions 0.8.5 and earlier, remote ZIP archives were …

CVE-2026-42274

Heimdall is a cloud native Identity Aware Proxy and Access Control Decision service. Prior to version 0.17.14, Heimdall performs rule …

CVE-2026-42273

Heimdall is a cloud native Identity Aware Proxy and Access Control Decision service. Prior to version 0.17.14, Heimdall performs host …

CVE-2026-42272

Heimdall is a cloud native Identity Aware Proxy and Access Control Decision service. Prior to version 0.17.14, Heimdall handles URL-encoded …

CVE-2025-25292 9.8

ruby-saml provides security assertion markup language (SAML) single sign-on (SSO) for Ruby. An authentication bypass vulnerability was found in ruby-saml …

CVE-2025-25291 9.8