Critical severity · published May 7, 2026
CVE-2026-8034
Server-side request forgery vulnerability in GitHub Enterprise Server notebook viewer via URL parser confusion
9.8
CVSS
0.5%
EPSS
No
On KEV
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 vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
Attack vector
Network
Complexity
Low
Privileges
None
User interaction
None
Confidentiality
High
Integrity
High
Availability
High
Scope
Unchanged
Exploitation
Is it being used?
Exploit prediction (EPSS)0.5% · higher than 44% of CVEs
Exploited in the wildNo evidence yet
CISA KEVNot listed
Ransomware campaign useNot known
Affected products
Which versions
ES
Enterprise Server · GitHub
3.16.0 through 3.16.17; 3.17.0 through 3.17.14; 3.18.0 through 3.18.8; 3.19.0 through 3.19.5; 3.20.0 through 3.20.1 · source: vendor, NVD
References
NVD
https://nvd.nist.gov/vuln/detail/CVE-2026-8034
CVE.org
https://www.cve.org/CVERecord?id=CVE-2026-8034
Release Notes
https://docs.github.com/en/enterprise-server@3.16/admin/release-notes#3.16.18
Release Notes
https://docs.github.com/en/enterprise-server@3.17/admin/release-notes#3.17.15
Release Notes
https://docs.github.com/en/enterprise-server@3.18/admin/release-notes#3.18.9
Release Notes
https://docs.github.com/en/enterprise-server@3.19/admin/release-notes#3.19.6
Release Notes
https://docs.github.com/en/enterprise-server@3.20/admin/release-notes#3.20.2
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