How severe is CVE-2026-1999?

CVE-2026-1999 has a CVSS 3.x base score of 6.5, rated medium severity. It is exploitable over network with low attack complexity, requires low privileges and no user interaction. Impact on confidentiality is none, integrity high, and availability none.

Is CVE-2026-1999 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 0% (14th percentile), an estimate of the probability of exploitation in the next 30 days.

What products are affected by CVE-2026-1999?

CVE-2026-1999 affects Github Enterprise Server. See the affected-products list for the exact vulnerable versions.

How do I fix CVE-2026-1999?

Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround.

Does CVE-2026-1999 have an EU (EUVD) identifier?

Yes. CVE-2026-1999 is tracked in the ENISA EU Vulnerability Database (EUVD) as EUVD-2026-7963.

When was CVE-2026-1999 published?

CVE-2026-1999 was published on 2026-02-18 and last updated on 2026-06-17.

CVE-2026-1999

CVE-2026-1999 is a medium-severity vulnerability in Github Enterprise Server with a CVSS 3.x base score of 6.5. It is not currently listed as actively exploited by CISA, and its EPSS exploit-prediction score is low. The underlying weakness is classified as CWE-863.

Key facts

Severity: Medium (CVSS 3.x base score 6.5)
CVSS v4: 7.1
EPSS exploit prediction: 0% (14th percentile)
Actively exploited: Not listed in CISA KEV
EU (EUVD) id: EUVD-2026-7963
Weakness: CWE-863
Affected product: Github Enterprise Server
Published: 2026-02-18
Last modified: 2026-06-17

Description

An incorrect authorization vulnerability was identified in GitHub Enterprise Server that allowed an attacker to merge their own pull request into a repository without having push access by exploiting an authorization bypass in the enable_auto_merge mutation for pull requests. This issue only affected repositories that allow forking as the attack relies on opening a pull request from an attacker-controlled fork into the target repository. Exploitation was only possible in specific scenarios. It required a clean pull request status and only applied to branches without branch protection rules enabled. This vulnerability affected GitHub Enterprise Server versions prior to 3.19.2, 3.18.5, and 3.17.11, and was fixed in versions 3.19.2, 3.18.5, and 3.17.11. This vulnerability was reported via the GitHub Bug Bounty program.

Frequently asked questions

What is CVE-2026-1999?: An incorrect authorization vulnerability was identified in GitHub Enterprise Server that allowed an attacker to merge their own pull request into a repository without having push access by exploiting an authorization bypass in the enable_auto_merge mutation for pull requests. This issue only affected repositories that allow forking as the attack relies on opening a pull request from an attacker-controlled fork into the target repository. Exploitation was only possible in specific scenarios. It required a clean pull request status and only applied to branches without branch protection rules enabled. This vulnerability affected GitHub Enterprise Server versions prior to 3.19.2, 3.18.5, and 3.17.11, and was fixed in versions 3.19.2, 3.18.5, and 3.17.11. This vulnerability was reported via the GitHub Bug Bounty program.
How severe is CVE-2026-1999?: CVE-2026-1999 has a CVSS 3.x base score of 6.5, rated medium severity. It is exploitable over network with low attack complexity, requires low privileges and no user interaction. Impact on confidentiality is none, integrity high, and availability none.
Is CVE-2026-1999 being actively exploited?: It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 0% (14th percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2026-1999?: CVE-2026-1999 affects Github Enterprise Server. See the affected-products list for the exact vulnerable versions.
How do I fix CVE-2026-1999?: Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround.
Does CVE-2026-1999 have an EU (EUVD) identifier?: Yes. CVE-2026-1999 is tracked in the ENISA EU Vulnerability Database (EUVD) as EUVD-2026-7963.
When was CVE-2026-1999 published?: CVE-2026-1999 was published on 2026-02-18 and last updated on 2026-06-17.

References

Affected products (1)

cpe:2.3:a:github:enterprise_server:*:*:*:*:*:*:*:*

More vulnerabilities in Github Enterprise Server

CVE-2026-8034 — Critical (CVSS 9.8): A server-side request forgery (SSRF) vulnerability was identified in the GitHub Enterprise Server notebook viewer that…
CVE-2024-6800 — Critical (CVSS 9.8): An XML signature wrapping vulnerability was present in GitHub Enterprise Server (GHES) when using SAML authentication…
CVE-2024-4985 — Critical (CVSS 9.8): An authentication bypass vulnerability was present in the GitHub Enterprise Server (GHES) when utilizing SAML single…
CVE-2022-23739 — Critical (CVSS 9.8): An incorrect authorization vulnerability was identified in GitHub Enterprise Server, allowing for escalation of…
CVE-2022-46255 — Critical (CVSS 9.8): An improper limitation of a pathname to a restricted directory vulnerability was identified in GitHub Enterprise Server…
CVE-2021-22869 — Critical (CVSS 9.8): An improper access control vulnerability in GitHub Enterprise Server allowed a workflow job to execute in a self-hosted…

All CVEs affecting Github Enterprise Server →

Other CWE-863 (Incorrect Authorization) vulnerabilities

CVE-2026-48286 — Critical (CVSS 10.0): Adobe Campaign Classic (ACC) versions 7.4.3 build 9396 and earlier are affected by an Incorrect Authorization…
CVE-2026-48303 — Critical (CVSS 10.0): Adobe Campaign Classic (ACC) versions 7.4.3 build 9394 and earlier are affected by an Incorrect Authorization…
CVE-2026-44330 — Critical (CVSS 10.0): free5GC is an open-source implementation of the 5G core network. Prior to 4.2.2, free5GC's NEF mounts the…
CVE-2026-46595 — Critical (CVSS 10.0): Previously, CVE-2024-45337 fixed an authorization bypass for misused ssh server configurations; if any other type of…
CVE-2026-33105 — Critical (CVSS 10.0): Improper authorization in Microsoft Azure Kubernetes Service allows an unauthorized attacker to elevate privileges over…
CVE-2026-32213 — Critical (CVSS 10.0): Improper authorization in Azure AI Foundry allows an unauthorized attacker to elevate privileges over a network.

Browse all CWE-863 (Incorrect Authorization) vulnerabilities →