(Serious Issue Of Github) Commit Timestamp Manipulation via Local System Clock Allows Fabricated Historical Commit Records

[vibhu-dixit-dev]

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Summary

I identified a vulnerability in GitHub’s commit timestamp validation logic where GitHub accepts commit timestamps based solely on the client’s local system clock without server-side verification. By changing the system date/time on a local machine before creating and pushing commits, it is possible to generate commits that appear to originate in the past or future. GitHub displays these manipulated timestamps in the repository history without distinguishing them from legitimate timestamps, potentially allowing commit history falsification.

Impact

This issue enables users to fabricate misleading chronological commit history. Potential abuses include:

• falsely claiming earlier authorship of code or ideas
• manipulating contribution graphs and activity timelines
• creating fraudulent evidence of work in professional, academic, or legal contexts
• undermining integrity of Git-based audit trails and project timelines
• Since commit metadata is widely used for proof-of-work, provenance, and due diligence validation, the absence of timestamp verification can be exploited to misrepresent contributions or sequence of events.

Steps to Reproduce

1. Change the system time and date on a local machine to an arbitrary past or future value.
2. Create a new commit in any GitHub repository.
3. Push the commit to GitHub.
4. Observe that GitHub displays the manipulated timestamp exactly as authored, without warning or correction.

Expected Behavior

GitHub should validate or normalize commit timestamps (e.g., using server time, trusted NTP, or flagging anomalous timestamps) to prevent arbitrary manipulation.

Actual Behavior

GitHub accepts the client-side timestamp verbatim, allowing creation of commits dated inaccurately relative to real time.

Proof of Concept

Example commit created with intentionally modified system time to demonstrate timestamp fabrication (details can be provided privately if required).

Severity Justification

This vulnerability affects:

1. data integrity
2. chronological trust
3. audit reliability

Because commit history is often used as evidence or as a timeline of authorship, the ability to falsify it without detection poses reputational, legal, and workflow risks.

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[JessMTermini]

This needs to be flagged and given more attention. You should also submit this bug thrhough their Bug Bounty Program or maybe even open a direct support ticket with github directly. I agree this IS SERIOUS.