CVE-2026-77987: A server-side request forgery (SSRF) vulnerability was identified in the notebook viewer of GitHub Enterprise

This month

CRITICAL 9.8REMOTEUPGRADE

CVE-2026-77987 is a critical-severity flaw (CVSS 9.8) affecting enterprise server. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

A server-side request forgery (SSRF) vulnerability was identified in the notebook viewer of GitHub Enterprise Server. The notebook viewer validated the scheme and host of a user-supplied URL but did not validate the port, allowing requests to be directed to internal services listening on other ports of the same appliance. Response bodies were not returned to the requester, but response timing acted as an oracle that allowed instance secrets to be

Why this priority

Critical severity
CISA SSVC: automatable with total technical impact
Remotely exploitable, no login, no user action

A fixed release or distro patch exists.

Risk facts

CVSS score	9.8 (Critical)
Attack vector	Network (remote)
Attack complexity	Low
Privileges needed	None
User interaction	None
EPSS exploit chance	0.9% (top 41%)
CISA exploited list	No
Weakness	CWE-208, CWE-918
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 18:37 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.

Exact fixes by distribution

Fedora 46 · fio · FIXED · 3.43-2.fc46 · FEDORA-2026-b36219886b · source

sudo dnf upgrade --advisory=FEDORA-2026-b36219886b

Fedora ELN · weston · FIXED · 16.0.2-1.eln159 · FEDORA-2026-b98ccaa6a0 · source

sudo dnf upgrade --advisory=FEDORA-2026-b98ccaa6a0

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-2026-77987?

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-2026-77987 being exploited?

CVE-2026-77987 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-2026-77987 affect?

CVE-2026-77987 affects enterprise server. Severity is critical (CVSS 9.8). A server-side request forgery (SSRF) vulnerability was identified in the notebook viewer of GitHub Enterprise Server. The notebook viewer validated the scheme and host of a user-supplied URL but did not validate the port, allowing requests

How urgent is CVE-2026-77987?

Priority 57/100. Critical severity; CISA SSVC: automatable with total technical impact; Remotely exploitable, no login, no user action

Software pages

GitHub vulnerabilities

Related CVEs

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
CVE-2026-8034 CRITICAL 9.8 UPGRADE A server-side request forgery (SSRF) vulnerability was identified in the GitHub Enterprise Server notebook vie
CVE-2026-7541 HIGH 7.5 UPGRADE A denial of service vulnerability was identified in GitHub Enterprise Server that allowed an unauthenticated a
CVE-2026-6736 MEDIUM 6.5 UPGRADE An authentication bypass vulnerability was identified in GitHub Enterprise Server that allowed an unauthentica

References

← Back to latest CVEs