CVE-2026-76851

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.

An authorization bypass vulnerability was identified in GitHub Enterprise Server that allowed any authenticated user of the instance to read the raw diff or patch of pull requests in private repositories without authorization. Access tokens for raw pull request diffs and patches were scoped to the repository name and pull request number rather than to a globally unique repository identifier, so an attacker who created a repository and pull request matching a target's repository name and pull request number could use a token for their own repository to retrieve the private pull request's contents. Exploitation required the attacker to know the target repository's name and a valid pull request number. This vulnerability affected all versions of GitHub Enterprise Server prior to 3.22 and was fixed in versions 3.17.21, 3.18.15, 3.19.12, 3.20.8, and 3.21.6. This vulnerability was reported via the GitHub Bug Bounty program.

A denial of service vulnerability was identified in GitHub Enterprise Server that allowed an unauthenticated attacker to cause service disruption by sending crafted requests with deeply nested JSON payloads to an unauthenticated API endpoint. The endpoint parsed user-controlled JSON request bodies without size or depth limits.

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 extracted character by character. An extracted secret could then be used in a separate interaction with an internal service to obtain remote code execution on the appliance. Exploitation required network access to the instance and was unauthenticated when private mode was disabled, or required any authenticated user when private mode was enabled. This vulnerability affected GitHub Enterprise Server versions 3.17 through 3.22 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 through the GitHub Bug Bounty program.

GitHub Enterprise Server before version 3.22 has a path traversal vulnerability that allows an unauthenticated attacker to delete arbitrary files and directories on the instance, including the entire user storage directory containing Git LFS objects, release assets, attachments, and avatars. Exploitation of the X-GitHub-Request-Id header without sanitization as a filesystem path segment leads to data deletion.

GitHub Enterprise Server prior to version 3.22 has an SSRF vulnerability in an upload endpoint that allows an unauthenticated attacker to send crafted requests to internal services. By injecting path traversal content into request parameters, an attacker can bypass the intended request flow and redirect internal API calls.

A time-of-check time-of-use race condition vulnerability was identified in GitHub Enterprise Server that allowed remote code execution. Exploitation required an authenticated user with write access to a repository and precise timing of concurrent upload requests. This vulnerability affected all versions of GitHub Enterprise Server prior to 3.22 and was fixed in versions 3.17.20, 3.18.14, 3.19.11, 3.20.7, and 3.21.5.

A server-side request forgery (SSRF) vulnerability was identified in GitHub Enterprise Server that allowed an unauthenticated attacker to cause the Manage API to send crafted outbound requests to an attacker-controlled host. The HMAC token authenticated only a timestamp, not the request path or body, so an attacker positioned to intercept the outbound request could capture and replay it against privileged management agent endpoints. High-availability deployments were not affected due to a topology restriction.

GitHub Enterprise Server before version 3.21 contains a denial of service vulnerability that allows an unauthenticated attacker to cause excessive CPU consumption and exhaust the pool of request-handling worker processes by sending a crafted form-encoded HTTP POST request with deeply nested parameters. The vulnerability was fixed in versions 3.20.3, 3.19.7, 3.18.10, and 3.17.16.

A missing authorization vulnerability in GitHub Enterprise Server allowed an authenticated user with write access to any repository to read metadata from private repositories they did not have access to. The flaw enabled enumeration of rule identifiers and disclosure of repository names, branch names, commit SHAs, commit messages, and the pushing actor.