Environment-variable disclosure via unchecked redirect destination
Published Apr 21, 2026 · Updated Apr 21, 2026
SSRF in GitHub Enterprise Server 3.14.0 through 3.20.0 allows remote attackers to infer environment variables through response timing. The notebook viewer follows HTTP redirects without revalidating each destination host, allowing requests to reach internal services and use regex-filter timing to infer values character by character. Exploitation requires private mode to be disabled plus a chain through the instance's open redirect and an external redirect; the bounded result is indirect disclosure of environment variables.
Summary
What happened
SSRF in GitHub Enterprise Server 3.14.0 through 3.20.0 allows remote attackers to infer environment variables through response timing. The notebook viewer follows HTTP redirects without revalidating each destination host, allowing requests to reach internal services and use regex-filter timing to infer values character by character. Exploitation requires private mode to be disabled plus a chain through the instance's open redirect and an external redirect; the bounded result is indirect disclosure of environment variables.
The record
- CVE
- CVE-2026-5921
- Published
- Apr 21, 2026
- Updated
- Apr 21, 2026
- Vendor
- Product
- GitHub Enterprise Server
- Classifications
- CWE-918, T1190
- Attack vector
- network
- Privileges
- unauthenticated
Timeline
How it unfolded
- Apr 21, 2026CVE publishedPublication date reported by the CVE source.
- Apr 21, 2026Record updatedLatest update available in the CVE record.
Exploitability
Present is not the same as exploitable
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Is a vulnerable build present?
Compare these published version ranges with your installed build and any vendor patches.
- Affected versionversion=3.14.0 <3.14.26 changes=[{"at":"3.14.26","status":"unaffected"}]
- Affected versionversion=3.15.0 <3.15.21 changes=[{"at":"3.15.21","status":"unaffected"}]
- Affected versionversion=3.16.0 <3.16.17 changes=[{"at":"3.16.17","status":"unaffected"}]
- Affected versionversion=3.17.0 <3.17.14 changes=[{"at":"3.17.14","status":"unaffected"}]
- Affected versionversion=3.18.0 <3.18.8 changes=[{"at":"3.18.8","status":"unaffected"}]
- Affected versionversion=3.19.0 <3.19.5 changes=[{"at":"3.19.5","status":"unaffected"}]
- Affected versionversion=3.20.0 <3.20.1 changes=[{"at":"3.20.1","status":"unaffected"}]
What conditions does exploitation require?
What is affected?
Published CVSS scores
CVSS describes severity. EPSS estimates exploitation probability.
Attacks
What attackers are doing with it
Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.
Weakness, pattern, technique
Public exploit references
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Technologies
Your stack
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Your stack
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