GitHub Enterprise Server EUVD-2026-40408

Q: What is the CVSS score of EUVD-2026-40408?

EUVD-2026-40408 has a CVSS 4.0 base score of 6.0 (Medium). CVSS vector: CVSS:4.0/AV:N/AC:L/AT:P/PR:L/UI:N/VC:H/VI:N/VA:N/SC:N/SI:N/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:X/R:X/V:X/RE:X/U:X. EPSS exploitation probability: 0.3%.

| CVE-2026-9132 MEDIUM

Missing Authorization (CWE-862)

2026-06-30 GitHub_P

GHSA-42pg-j2h8-h5fw

Authentication Bypass Enterprise Server

6.0

CVSS 4.0 · Vendor: GitHub_P

Severity by source

Vendor (GitHub_P) PRIMARY

6.0 MEDIUM

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

vuln.today AI

6.5 MEDIUM

Network-reachable endpoint requires low-privilege authenticated session (PR:L); no scope change as both vulnerable component and impacted data reside within the same GHES instance; high confidentiality loss, no integrity or availability impact.

3.1 AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:N

4.0 AV:N/AC:L/AT:P/PR:L/UI:N/VC:H/VI:N/VA:N/SC:N/SI:N/SA:N

Primary rating from Vendor (GitHub_P).

CVSS VectorVendor: GitHub_P

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

Attack Vector

Network

Attack Complexity

Low

Privileges Required

Low

User Interaction

None

Scope

Lifecycle Timeline

Analysis Generated

Jun 30, 2026 - 21:21 vuln.today

DescriptionCVE.org

A missing authorization vulnerability was identified in GitHub Enterprise Server that allowed an authenticated user to read source code from private repositories they did not have access to. The Copilot pull request description diff summary endpoint accepted a cross-repository comparison range and rendered the resulting diff without verifying that the requesting user was authorized to view the target repository. Exploitation required an authenticated account on the instance with read access to at least one repository to use as the comparison base. This vulnerability affected all versions of GitHub Enterprise Server prior to 3.21 and was fixed in versions 3.17.17, 3.18.11, 3.19.8, and 3.20.4. This vulnerability was reported via the GitHub Bug Bounty program.

AnalysisAI

Unauthorized source code disclosure in GitHub Enterprise Server exposes private repository contents to any authenticated user on the instance, regardless of their actual repository permissions. The Copilot pull request description diff summary endpoint accepted cross-repository comparison ranges and rendered the resulting diff without verifying the requesting user held read access to the target repository - a missing authorization flaw (CWE-862) allowing lateral access to arbitrary private repositories. No active exploitation has been confirmed (not in CISA KEV), the issue was responsibly disclosed via GitHub's Bug Bounty program, and patches are available across four release branches.

Technical ContextAI

GitHub Enterprise Server (GHES) is a self-hosted deployment of GitHub's platform for enterprise environments, distinct from GitHub.com. The vulnerability is rooted in the Copilot-powered pull request description feature, which invokes a diff summary endpoint to generate AI-assisted PR descriptions. This endpoint accepts a cross-repository comparison range parameter - allowing a caller to specify a source and target repository for the diff - but only enforced authorization checks on the source (base) repository. The target repository authorization was entirely absent, a textbook CWE-862 (Missing Authorization) failure where a security-sensitive function executes without verifying the caller's permission on the accessed resource. CPE string cpe:2.3:a:github:enterprise_server:*:*:*:*:*:*:*:* confirms the scope is limited to self-hosted GHES instances; the CVSS 4.0 AT:P metric reflects that exploitation depends on the attacker already holding a valid authenticated session with at least one repository's read access.

RemediationAI

The primary remediation is to upgrade GitHub Enterprise Server to a patched release: 3.17.17, 3.18.11, 3.19.8, or 3.20.4, as documented in GitHub's official release notes linked in the references above. As a compensating control for organizations that cannot patch immediately, administrators should consider disabling the Copilot pull request description feature at the instance or organization level to eliminate exposure of the vulnerable endpoint; the trade-off is loss of AI-assisted PR description generation for all users. Additionally, auditing and restricting which accounts hold any repository access on the instance reduces the exploitable population - removing dormant, contractor, or untrusted accounts that no longer require access directly shrinks the attack surface. These controls do not remediate the root flaw and should be treated as temporary measures pending the patch upgrade.