Stored cross-site scripting vulnerability in GitHub Enterprise Server allowed HTML attribute injection via the Markdown rendering pipeline

MITRE NVD CVE.ORG JSON API

Summary

CVECVE-2026-77912
StatePUBLISHED
AssignerGitHub_P
Source PriorityCVE Program / NVD first with legacy fallback
Published2026-09-22 21:17:32 UTC
Updated2026-10-02 18:38:48 UTC
DescriptionA stored cross-site scripting (XSS) vulnerability was identified in GitHub Enterprise Server that allowed an authenticated attacker to inject arbitrary HTML attributes into rendered Markdown because the Markdown rendering pipeline rewrote quote characters in already-sanitized HTML without re-sanitizing the result. Crafted Markdown could abuse same-origin JavaScript gadgets to bypass Content Security Policy and gain control of the page DOM when viewed by another user. Successful exploitation could allow an attacker to read content visible to the victim, extract embedded CSRF tokens, perform state-changing actions as the victim, and exfiltrate data through same-origin writes. The payload could also propagate to repositories and organizations where the victim had write access. This vulnerability affected supported GitHub Enterprise Server releases in the 3.17, 3.18, 3.19, 3.20, 3.21, and 3.22 series and was fixed in versions 3.22.1, 3.21.6, 3.20.8, 3.19.12, 3.18.15, and 3.17.21. This vulnerability was reported via the GitHub Bug Bounty program.

Risk And Classification

Primary CVSS: v4.0 7.4 HIGH from [email protected]

CVSS:4.0/AV:N/AC:H/AT:N/PR:L/UI:P/VC:H/VI:H/VA:N/SC:L/SI:L/SA:N/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:Y/R:X/V:X/RE:X/U:X

EPSS: 0.004500000 probability, percentile 0.364880000 (date 2026-09-25)

Problem Types: CWE-79 | CWE-79 CWE-79 Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')

VersionSourceTypeScoreSeverityVector
4.0[email protected]Secondary7.4HIGHCVSS:4.0/AV:N/AC:H/AT:N/PR:L/UI:P/VC:H/VI:H/VA:N/SC:L/SI:L/SA:N/E:X/C...
4.0CNACVSS7.4HIGHCVSS:4.0/AV:N/AC:H/AT:N/PR:L/UI:P/VC:H/VI:H/VA:N/SC:L/SI:L/SA:N/AU:Y
3.1[email protected]Primary5.4MEDIUMCVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:C/C:L/I:L/A:N

CVSS v4.0 Breakdown

Attack Vector
Network
Attack Complexity
High
Attack Requirements
None
Privileges Required
Low
User Interaction
Passive
Confidentiality
High
Integrity
High
Availability
None
Sub Conf.
Low
Sub Integrity
Low
Sub Availability
None

CVSS:4.0/AV:N/AC:H/AT:N/PR:L/UI:P/VC:H/VI:H/VA:N/SC:L/SI:L/SA:N/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:Y/R:X/V:X/RE:X/U:X

CVSS v3.1 Breakdown

Attack Vector
Network
Attack Complexity
Low
Privileges Required
Low
User Interaction
Required
Scope
Changed
Confidentiality
Low
Integrity
Low
Availability
None

CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:C/C:L/I:L/A:N

NVD Known Affected Configurations (CPE 2.3)

TypeVendorProductVersionUpdateEditionLanguage
Application Github Enterprise Server All All All All

Vendor Declared Affected Products

SourceVendorProductVersionPlatforms
CNA GitHub Enterprise Server affected 3.17.0 3.17.* semver Not specified
CNA GitHub Enterprise Server affected 3.18.0 3.18.* semver Not specified
CNA GitHub Enterprise Server affected 3.19.0 3.19.* semver Not specified
CNA GitHub Enterprise Server affected 3.20.0 3.20.* semver Not specified
CNA GitHub Enterprise Server affected 3.21.0 3.21.* semver Not specified
CNA GitHub Enterprise Server affected 3.22.0 3.22.* semver Not specified

References

ReferenceSourceLinkTags
docs.github.com/en/[email protected]/admin/release-notes [email protected] docs.github.com Release Notes, Vendor Advisory
docs.github.com/en/[email protected]/admin/release-notes [email protected] docs.github.com Release Notes, Vendor Advisory
docs.github.com/en/[email protected]/admin/release-notes [email protected] docs.github.com Release Notes, Vendor Advisory
docs.github.com/en/[email protected]/admin/release-notes [email protected] docs.github.com Release Notes, Vendor Advisory
docs.github.com/en/[email protected]/admin/release-notes [email protected] docs.github.com Release Notes, Vendor Advisory
docs.github.com/en/[email protected]/admin/release-notes [email protected] docs.github.com Release Notes, Vendor Advisory
CVE Program record CVE.ORG www.cve.org canonical
NVD vulnerability detail NVD nvd.nist.gov canonical, analysis

Vendor Comments And Credit

Discovery Credit

CNA: ahacker1 (en)

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