EUVD-2026-24554
GHSA-2gr8-2hf5-x695
Severity by source
CVSS:4.0/AV:N/AC:H/AT:P/PR:N/UI:N/VC:H/VI:H/VA:L/SC:H/SI:H/SA:L/E:P/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
Unauthenticated network SSRF (PR:N/AV:N) crossing into internal services changes scope (S:C); the timing side-channel plus redirect and config prerequisites make it high complexity (AC:H); impact is chiefly secret disclosure (C:H) with minor integrity and no availability effect.
Primary rating from GitHub Advisory.
CVSS VectorGitHub Advisory
Lifecycle Timeline
5DescriptionGitHub Advisory
A server-side request forgery (SSRF) vulnerability was identified in GitHub Enterprise Server that allowed an attacker to extract sensitive environment variables from the instance through a timing side-channel attack against the notebook rendering service. When private mode was disabled, the notebook viewer followed HTTP redirects without revalidating the destination host, enabling an unauthenticated SSRF to internal services. By chaining this with regex filter queries against an internal API and measuring response time differences, an attacker could infer secret values character by character. Exploitation required that private mode be disabled and that the attacker be able to chain the instance's open redirect endpoint through an external redirect to reach internal services. This vulnerability affected all versions of GitHub Enterprise Server prior to 3.21 and was fixed in versions 3.14.26, 3.15.21, 3.16.17, 3.17.14, 3.18.8, 3.19.5, and 3.20.1. This vulnerability was reported via the GitHub Bug Bounty program.
AnalysisAI
Information disclosure via server-side request forgery in GitHub Enterprise Server (all versions prior to 3.21) lets an unauthenticated attacker read sensitive environment variables from the appliance. The notebook rendering service follows HTTP redirects without revalidating the destination host, so an attacker who chains the instance's open-redirect endpoint can reach internal services and, using regex filter queries against an internal API combined with response-timing measurement, exfiltrate secret values one character at a time. No public exploit is identified at time of analysis and EPSS is very low (0.05%), but SSVC rates the technical impact as total.
Technical ContextAI
The root cause is CWE-918 (SSRF): the notebook viewer acts as an HTTP client and follows redirects without re-checking that the final host is permitted, allowing requests to be pivoted to internal-only services. The affected product per CPE is cpe:2.3:a:github:enterprise_server across all pre-3.21 branches (3.14 through 3.20.0). The exploit is amplified by an Open Redirect (per the tags) used to bounce an external request into the internal network, and by a timing side-channel: a regex filter query against an internal API returns measurably different response times depending on whether a guessed character matches, enabling character-by-character inference of secrets rather than a direct read.
RemediationAI
Vendor-released patch: upgrade to the fixed release for your branch, one of 3.14.26, 3.15.21, 3.16.17, 3.17.14, 3.18.8, 3.19.5, or 3.20.1 (all pre-3.21 branches are affected); see the vendor release notes, e.g. https://docs.github.com/en/enterprise-server@3.20/admin/release-notes#3.20.1. As a compensating control until patched, enable private mode, which removes the primary precondition for exploitation and makes the SSRF path unreachable, at the trade-off of removing unauthenticated/anonymous access to the instance. Additionally restrict the appliance's outbound and internal egress so the notebook service cannot reach internal management APIs, and place the instance behind network controls that limit who can trigger the open-redirect endpoint; the trade-off is possible disruption to legitimate integrations that rely on outbound requests.
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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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