CVE-2026-77912: A stored cross-site scripting (XSS) vulnerability was identified in GitHub Enterprise Server that allowed an a

Routine

MEDIUM 5.4UPGRADE

CVE-2026-77912 is a medium-severity flaw (CVSS 5.4) affecting enterprise server. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

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 vi

Why this priority

No elevated risk signals yet

A fixed release or distro patch exists.

Risk facts

CVSS score	5.4 (Medium)
Attack vector	Network (remote)
Attack complexity	Low
Privileges needed	Low
User interaction	Required
EPSS exploit chance	0.2% (top 89%)
CISA exploited list	No
Weakness	CWE-79
Published	2026-09-22
Last modified	2026-10-02

Publisher (CNA): GitHub, Inc. (Products Only) · Vendor: github

Last updated 2026-10-02 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score

Am I affected?

Timeline

2026-09-22 21:17 UTCPublished CVE record published
2026-10-02 18:38 UTCUpdated Record last modified

github enterprise server UPGRADE

Affected: >= 3.17.0 and < 3.17.21 · >= 3.18.0 and < 3.18.15 · >= 3.19.0 and < 3.19.12 · >= 3.20.0 and < 3.20.8 · >= 3.21.0 and < 3.21.6 · >= 3.22.0 and < 3.22.1

Fixed in: 3.17.21, 3.18.15, 3.19.12, 3.20.8, 3.21.6, 3.22.1

Safe to downgrade to: a release before 3.17.0

1. Check installed version

apt-cache policy enterprise-server || rpm -q enterprise-server || enterprise-server --version

2. UPGRADE to 3.17.21 (Debian / Ubuntu)

sudo apt update && sudo apt install --only-upgrade enterprise-server

2. UPGRADE (RHEL / Amazon Linux / Fedora)

sudo dnf upgrade enterprise-server

Note

Distros often backport fixes without changing the version number. Confirm with the distro advisory or changelog.

3. If no update is available yet, DOWNGRADE to a release before 3.17.0 (Debian / Ubuntu)

apt-cache madison enterprise-server sudo apt install enterprise-server=<VERSION_BEFORE_3.17.0> sudo apt-mark hold enterprise-server

3. If no update is available yet, DOWNGRADE (RHEL / Amazon Linux / Fedora)

dnf --showduplicates list enterprise-server sudo dnf downgrade enterprise-server-<VERSION_BEFORE_3.17.0> sudo dnf versionlock add enterprise-server

Downgrade risk

Downgrading can break dependent software and may reopen older bugs. Read the distro advisory first and test on a non-production host.

After downgrade

Restart the service, and keep the package held until a fixed release ships.

Verify at the official source NVD · CVE Program · Report a problem with this page
Scores and fixes here are computed automatically from those and other public sources. Confirm with the vendor advisory before changing production systems.

Quick answers

How do I fix CVE-2026-77912?

enterprise server: upgrade to 3.17.21, 3.18.15, 3.19.12, 3.20.8, 3.21.6, 3.22.1. Exact commands for each OS are on this page.

Is CVE-2026-77912 being exploited?

CVE-2026-77912 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.

What does CVE-2026-77912 affect?

CVE-2026-77912 affects enterprise server. Severity is medium (CVSS 5.4). 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 q

How urgent is CVE-2026-77912?

Priority 22/100. No elevated risk signals yet.

Software pages

GitHub vulnerabilities

Related CVEs

CVE-2026-5921 HIGH 8.9 UPGRADE A server-side request forgery (SSRF) vulnerability was identified in GitHub Enterprise Server that allowed an
CVE-2026-4296 HIGH 8.8 UPGRADE An incorrect regular expression vulnerability was identified in GitHub Enterprise Server that allowed an attac
CVE-2026-3307 LOW 2.7 UPGRADE An authorization bypass vulnerability was identified in GitHub Enterprise Server that allowed an attacker with
CVE-2026-5845 CRITICAL 9.6 UPGRADE An improper authorization vulnerability in scoped user-to-server (ghu_) token authorization in GitHub Enterpri
CVE-2026-5512 MEDIUM 4.3 UPGRADE An improper authorization vulnerability was identified in GitHub Enterprise Server that allowed an authenticat

References

← Back to latest CVEs