# CVE-2026-39855: osslsigncode has an Integer Underflow in PE Page Hash Calculation Can Cause Out-of-Bounds Read

> An integer underflow in osslsigncode allows attackers to cause an out-of-bounds read and crash the application by providing a malicious PE file.

- **Severity:** Medium 5.5 (`CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:N/I:N/A:H`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Local or same network only
- **Victim action needed:** A user has to click or open something
- **Fix available:** Yes
- **Published:** 9 Apr 2026
- **Updated:** 9 Apr 2026
- **Also known as:** DEBIAN-CVE-2026-39855, GHSA-76vv-x5rr-q3mr, UBUNTU-CVE-2026-39855

## What is CVE-2026-39855?

CVE-2026-39855 is a medium-severity vulnerability in mtrojnar osslsigncode, published on 9 Apr 2026. It can only be exploited from the same machine or local network, and only if a user opens a file or follows a link.

### Official description

osslsigncode is a tool that implements Authenticode signing and timestamping. Prior to 2.13, an integer underflow vulnerability exists in osslsigncode version 2.12 and earlier in the PE page-hash computation code (pe_page_hash_calc()). When page hash processing is performed on a PE file, the function subtracts hdrsize from pagesize without first validating that pagesize >= hdrsize. If a malicious PE file sets SizeOfHeaders (hdrsize) larger than SectionAlignment (pagesize), the subtraction underflows and produces a very large unsigned length. The code allocates a zero-filled buffer of pagesize bytes and then attempts to hash pagesize - hdrsize bytes from that buffer. After the underflow, this results in an out-of-bounds read from the heap and can crash 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.

Weakness: CWE-191 (Integer Underflow (Wrap or Wraparound)), CWE-190 (Integer Overflow or Wraparound), CWE-125 (Out-of-bounds Read)

## Which versions are affected by CVE-2026-39855?

It affects 1 product.


Products: Osslsigncode Project Osslsigncode.

## How do I fix CVE-2026-39855?

Upgrade to a fixed version.

## Is CVE-2026-39855 being exploited?

There is no known exploitation of CVE-2026-39855 in the wild and no public exploit code.

## Other vulnerabilities in mtrojnar osslsigncode

- [CVE-2025-70888](https://insights.sbomify.com/CVE-2025-70888/): Privilege escalation in n/a (critical 9.8)
- [CVE-2026-39853](https://insights.sbomify.com/CVE-2026-39853/): osslsigncode has a Stack Buffer Overflow via Unbounded Digest Copy During Signature Verification (high 7.8)
- [CVE-2023-36377](https://insights.sbomify.com/CVE-2023-36377/): Memory corruption in n/a (high 7.8)
- [CVE-2026-39856](https://insights.sbomify.com/CVE-2026-39856/): osslsigncode has an Out-of-Bounds Read via Unvalidated Section Bounds in PE Page Hash Calculation (medium 5.5)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-39855 and fix it if it is affected.

What it is: CVE-2026-39855 is a medium-severity vulnerability in mtrojnar osslsigncode, published on 9 Apr 2026. It can only be exploited from the same machine or local network, and only if a user opens a file or follows a link.
Exploitation: There is no known exploitation of CVE-2026-39855 in the wild and no public exploit code.

Affected product: mtrojnar osslsigncode. No package-level version data is available, so check the vendor advisory linked from the reference page.

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-39855/ (Markdown: https://insights.sbomify.com/CVE-2026-39855/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-39855
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-39855
- OSV: https://osv.dev/vulnerability/CVE-2026-39855

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-39855/
Summaries are generated and may contain mistakes; the official description above is the record.