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.
- 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
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.
Which versions are affected by CVE-2026-39853?
It affects 1 product.
Products include Osslsigncode Project Osslsigncode.
How do I fix CVE-2026-39853?
Upgrade to a fixed version.
Upgrade to the fixed version. Memory-safe languages, compiler hardening and fuzzing prevent most new cases. More about Memory corruption.
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 Privilege escalation in n/a
- CVE-2023-36377 Memory corruption in n/a
- CVE-2026-39855 osslsigncode has an Integer Underflow in PE Page Hash Calculation Can Cause Out-of-Bounds Read
- CVE-2026-39856 osslsigncode has an Out-of-Bounds Read via Unvalidated Section Bounds in PE Page Hash Calculation
Sources
Also known as DEBIAN-CVE-2026-39853, GHSA-hx87-8754-xvh4, UBUNTU-CVE-2026-39853.