{"cve":"CVE-2026-5921","nvd":{"published":"2026-04-21T23:16:22.667","modified":"2026-10-26T22:10:00.163","status":"Analyzed","description":"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.","cvss_v4":{"vector":"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","score":8.9},"cvss_v3":{"version":"3.1","vector":"CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:C/C:H/I:H/A:L","score":8.9},"cwes":["CWE-918"],"references":["https://docs.github.com/en/enterprise-server@3.14/admin/release-notes#3.14.26","https://docs.github.com/en/enterprise-server@3.15/admin/release-notes#3.15.21","https://docs.github.com/en/enterprise-server@3.16/admin/release-notes#3.16.17","https://docs.github.com/en/enterprise-server@3.17/admin/release-notes#3.17.14","https://docs.github.com/en/enterprise-server@3.18/admin/release-notes#3.18.8"],"products":["github:enterprise_server"],"source":"nvd","synced_at":"2026-10-26T22:26:44.656832877+00:00"},"epss":{"cve":"CVE-2026-5921","score":0.00424,"percentile":0.36436,"date":"2026-10-26"},"kev":null,"osv":[],"attribution":["This product uses the NVD API but is not endorsed or certified by the NVD.","EPSS scores: FIRST Exploit Prediction Scoring System, https://www.first.org/epss","Known exploited vulnerabilities: CISA Known Exploited Vulnerabilities Catalog, https://www.cisa.gov/known-exploited-vulnerabilities-catalog","Package advisories: OSV (https://osv.dev), from the GitHub Advisory Database, PyPA, Go, RustSec and other ecosystem databases, under CC-BY 4.0 or CC0","CVE records: the CVE Program's CVE List (https://www.cve.org), under its terms of use (https://www.cve.org/Legal/TermsOfUse). CVE is a registered trademark of The MITRE Corporation; this product is not affiliated with the CVE Program."]}