EUVD-2026-28464
GHSA-w548-vv26-rff6
Severity by source
CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:N/SC:H/SI:H/SA:H/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X
Primary rating from GitHub Advisory · only source for this CVE.
CVSS VectorGitHub Advisory
CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:N/SC:H/SI:H/SA:H/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X
Lifecycle Timeline
4DescriptionGitHub Advisory
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.
AnalysisAI
Server-side request forgery in GitHub Enterprise Server's notebook viewer enables remote unauthenticated attackers to access internal services and systems through URL parser confusion. The vulnerability exploits discrepancies between validation and request execution parsers, allowing crafted URLs to bypass hostname checks and target unintended internal hosts. All versions prior to 3.21 are affected, with patches available across supported release branches (3.16.18, 3.17.15, 3.18.9, 3.19.6, 3.20.2). CVSS 7.9 reflects high impact to subsequent system confidentiality, integrity, and availability. No active exploitation confirmed (not in CISA KEV); reported through GitHub Bug Bounty program.
Technical ContextAI
This is a classic SSRF vulnerability (CWE-918) arising from URL parser differential behavior. GitHub Enterprise Server's notebook viewer implements hostname validation using one URL parsing library, while the HTTP request execution layer uses a different parser. This architectural mismatch creates opportunities for parser confusion attacks where specially crafted URLs are interpreted differently by each component. The validation layer may parse a URL as targeting an approved external host, while the request library interprets the same URL as targeting internal infrastructure (RFC 3986 parsing ambiguities, encoding differences, or handling of edge cases like authority section parsing). The affected component is specifically the notebook viewer feature, suggesting Jupyter or similar notebook rendering functionality that fetches remote resources. The CVSS:4.0 vector shows no impact to the vulnerable system itself (VC:N/VI:N/VA:N) but high impact to subsequent systems (SC:H/SI:H/SA:H), accurately reflecting SSRF where the exploited service becomes a pivot point to attack internal resources.
RemediationAI
Upgrade GitHub Enterprise Server to patched versions: 3.16.18, 3.17.15, 3.18.9, 3.19.6, or 3.20.2 depending on current release branch, or migrate to version 3.21.0 or later. Official release notes with upgrade instructions available at https://docs.github.com/en/enterprise-server@3.16/admin/release-notes#3.16.18 (and corresponding URLs for other versions). Organizations unable to immediately patch should implement network-level egress controls restricting the GitHub Enterprise Server instance from accessing internal network ranges (RFC 1918 private addresses, link-local addresses, cloud metadata endpoints at 169.254.169.254, localhost/loopback). Consider disabling the notebook viewer feature if not operationally required, though specific configuration instructions are not detailed in available advisories. Deploy web application firewall rules to detect and block SSRF patterns in requests to notebook viewer endpoints, though this provides defense-in-depth only and may be bypassed by sophisticated encoding techniques. Network segmentation should isolate GitHub Enterprise Server from sensitive internal services as compensating control, though this may impact legitimate integrations requiring internal connectivity.
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Same weakness CWE-918 – Server-Side Request Forgery (SSRF)
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External POC / Exploit Code
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