# CVE-2026-77912: Stored cross-site scripting vulnerability in GitHub Enterprise Server allowed HTML attribute injection via the Markdown rendering pipeline

> CVE-2026-77912: Stored cross-site scripting vulnerability in GitHub Enterprise Server allowed HTML attribute injection via the Markdown rendering pipeline. CVSS 5.4 (CVSS 3.1).

Canonical: https://rewindex.com/cve/CVE-2026-77912
Last updated: 2026-10-02T18:38:48Z

- Published: 2026-09-22 20:43 UTC · Updated: 2026-10-02 18:38 UTC · Assigner: GitHub\_P
- CVSS: 5.4 (CVSS 3.1) · Severity: Medium · Vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:C/C:L/I:L/A:N
- EPSS: 0.21%, 11th percentile (scored 2026-10-25)
- CISA KEV: no
- CWE: CWE-79

## Description

A 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.

## Affected vendors and products

- GitHub: Enterprise Server

## Tracked companies

- [GitHub](https://rewindex.com/company/github.md)

## References

- [CVE record on cve.org](https://www.cve.org/CVERecord?id=CVE-2026-77912)
- [NVD entry](https://nvd.nist.gov/vuln/detail/CVE-2026-77912)
- [https://docs.github.com/en/enterprise-server@3.17/admin/release-notes\#3.17.21](https://docs.github.com/en/enterprise-server@3.17/admin/release-notes#3.17.21)
- [https://docs.github.com/en/enterprise-server@3.18/admin/release-notes\#3.18.15](https://docs.github.com/en/enterprise-server@3.18/admin/release-notes#3.18.15)
- [https://docs.github.com/en/enterprise-server@3.19/admin/release-notes\#3.19.12](https://docs.github.com/en/enterprise-server@3.19/admin/release-notes#3.19.12)
- [https://docs.github.com/en/enterprise-server@3.20/admin/release-notes\#3.20.8](https://docs.github.com/en/enterprise-server@3.20/admin/release-notes#3.20.8)
- [https://docs.github.com/en/enterprise-server@3.21/admin/release-notes\#3.21.6](https://docs.github.com/en/enterprise-server@3.21/admin/release-notes#3.21.6)
- [https://docs.github.com/en/enterprise-server@3.22/admin/release-notes\#3.22.1](https://docs.github.com/en/enterprise-server@3.22/admin/release-notes#3.22.1)

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_Sources: CVE records from the CVE Program (cve.org). CVE® is a registered trademark of The MITRE Corporation. (https://www.cve.org/) This product uses data from the NVD API but is not endorsed or certified by the NVD. (https://nvd.nist.gov/) Known Exploited Vulnerabilities catalog from CISA. (https://www.cisa.gov/known-exploited-vulnerabilities-catalog) EPSS scores from FIRST (Exploit Prediction Scoring System). (https://www.first.org/epss/)_


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Canonical: https://rewindex.com/cve/CVE-2026-77912 · Markdown: https://rewindex.com/cve/CVE-2026-77912.md · JSON: https://rewindex.com/api/v1/cves/CVE-2026-77912 · Data licensed CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/) · Generated 2026-10-26T04:04:10.952Z