# CVE-2026-39853: osslsigncode has a Stack Buffer Overflow via Unbounded Digest Copy During Signature Verification

> Attackers can execute arbitrary code by tricking users into verifying maliciously crafted signed files with oversized digest fields.

- **Severity:** High 7.8 (`CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:H/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-2026-39853, GHSA-hx87-8754-xvh4, UBUNTU-CVE-2026-39853

## What is CVE-2026-39853?

CVE-2026-39853 is a high-severity memory corruption 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 2.12, A stack buffer overflow vulnerability exists in osslsigncode in several signature verification paths. During verification of a PKCS#7 signature, the code copies the digest value from a parsed SpcIndirectDataContent structure into a fixed-size stack buffer  (mdbuf[EVP_MAX_MD_SIZE], 64 bytes) without validating that the source length fits within the destination buffer. This pattern is present in the verification handlers for PE, MSI, CAB, and script files. An attacker can craft a malicious signed file with an oversized digest field in SpcIndirectDataContent. When a user verifies such a file with osslsigncode verify, the unbounded memcpy can overflow the stack buffer and corrupt adjacent stack state. This vulnerability is fixed in 2.12.

Weakness: CWE-787 (Out-of-bounds Write), CWE-121 (Stack-based Buffer Overflow)

## Which versions are affected by CVE-2026-39853?

It affects 1 product.


Products: Osslsigncode Project Osslsigncode.

## How do I fix CVE-2026-39853?

Upgrade to a fixed version.

## Is CVE-2026-39853 being exploited?

There is no known exploitation of CVE-2026-39853 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-2023-36377](https://insights.sbomify.com/CVE-2023-36377/): Memory corruption in n/a (high 7.8)
- [CVE-2026-39855](https://insights.sbomify.com/CVE-2026-39855/): osslsigncode has an Integer Underflow in PE Page Hash Calculation Can Cause Out-of-Bounds Read (medium 5.5)
- [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-2026-39853 and fix it if it is affected.

What it is: CVE-2026-39853 is a high-severity memory corruption 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-2026-39853 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-2026-39853/ (Markdown: https://insights.sbomify.com/CVE-2026-39853/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-39853
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-39853
- OSV: https://osv.dev/vulnerability/CVE-2026-39853

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From sbomify Insights: https://insights.sbomify.com/CVE-2026-39853/
Summaries are generated and may contain mistakes; the official description above is the record.