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CVE-2026-3854 is a critical remote code execution vulnerability discovered in the GitHub Enterprise Server (GHES) push pipeline.
The vulnerability arises from a trust-boundary failure where client-supplied git push options are serialized into internal metadata headers.
Specifically, internal routing and proxy daemons encode user-submitted push options into semicolon-delimited key-value strings known as the X-Stat header.
When parsing this header, the internal system relies on last-write-wins semantics without escaping or sanitizing delimiter characters.
An authenticated user with push permissions can craft malicious push options containing semicolon separators to inject arbitrary internal configuration variables.
By exploiting this parser flaw, attackers can manipulate security-sensitive parameters like rails_env, custom_hooks_dir, and repo_pre_receive_hooks.
This injection primitive allows overriding production sandbox paths and redirecting hook execution directories to arbitrary locations on the filesystem.
Chaining these three distinct configuration injections enables unprivileged users to execute arbitrary binaries directly as the git service user.
Consequently, an attacker who can push to a single repository can leverage this execution context to compromise the entire GHES instance.
The vulnerability highlights the critical danger of allowing user-controlled protocol inputs to merge seamlessly into trusted internal metadata channels.
Mitigation requires updating GHES to the officially patched versions provided by GitHub to neutralize the parser ambiguity and secure hook execution.
DailyCVE Form:
Platform: GitHub Enterprise Server
Version: Prior to patched
Vulnerability: Push Option Injection
Severity: Critical Risk
Date: March 2026
Prediction: Released April 2026
What Undercode Say:
When inspecting the push pipeline handling, the core issue lies in how internal daemons process the X-Stat metadata header.
Developers must ensure that client-supplied parameters like git push options are strictly segregated from internal control structures.
Below are sample interaction commands used to demonstrate the mechanics of the push option injection vector during local testing:
git push -o 'rails_env=development' -o 'custom_hooks_dir=/tmp' origin master git push -o 'repo_pre_receive_hooks=../../bin/sh' origin master
Ensure proper input validation and delimiter encoding are enforced across all internal microservice boundaries to prevent metadata overrides.
Exploit: (Educational Purposes!)
The exploitation mechanism involves constructing a crafted git push command containing injected key-value pairs that target internal parsing logic.
By passing malformed push options with delimiter characters, the internal proxy fails to neutralize special elements, allowing parameter pollution.
The attack sequence overrides sandbox environment variables and redirects pre-receive hooks to execute system binaries under the git user context.
git push -o 'user_operator_mode=bool:true' -o 'custom_hooks_dir=/attacker/path' origin main
Execution results in arbitrary command execution without requiring administrative privileges on the target instance.
Protection: from this CVE
Administrators must immediately upgrade GitHub Enterprise Server instances to the patched versions released by GitHub.
Review system audit logs, specifically /var/log/github-audit.log, for any push operations containing semicolon characters in push options.
Rotate potentially compromised secrets, credentials, and internal service tokens if unauthorized push activities are detected.
Enforce strict access controls and monitor repository push permissions across enterprise environments.
Impact:
Successful exploitation grants remote code execution as the unprivileged git service user on the affected GitHub Enterprise Server instance.
This level of access allows attackers to read repository contents, inspect internal configurations, and potentially pivot across tenants.
The integrity and confidentiality of self-hosted enterprise codebases are severely compromised, threatening entire development pipelines.
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Sources:
Reported By: github.com
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