Vulnerability · Published Apr 9, 2026 · Assigned by GitHub_M
CVE-2026-39853osslsigncode has a Stack Buffer Overflow via Unbounded Digest Copy During Signature Verification
High 7.8
In plain English
A high-severity stack buffer overflow in osslsigncode from mtrojnar. There are no confirmed reports of exploitation so far. The chance it is exploited in the next 30 days is estimated at 0.2% (higher than 6% of all known vulnerabilities). Fixed versions are available - upgrade the affected package.
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.
Affected packages & fixed versions
| Ecosystem | Package | Fixed in | Advisory |
|---|---|---|---|
| Debian:12 | osslsigncode | no fix listed | DEBIAN-CVE-2026-39853 |
| Debian:13 | osslsigncode | no fix listed | DEBIAN-CVE-2026-39853 |
| Debian:14 | osslsigncode | 2.12-1 | DEBIAN-CVE-2026-39853 |
| Ubuntu:22.04:LTS | osslsigncode | no fix listed | UBUNTU-CVE-2026-39853 |
| Ubuntu:24.04:LTS | osslsigncode | no fix listed | UBUNTU-CVE-2026-39853 |
| Ubuntu:25.10 | osslsigncode | no fix listed | UBUNTU-CVE-2026-39853 |
Affected products (as reported)
| Vendor | Product | Versions |
|---|---|---|
| mtrojnar | osslsigncode | < 2.12 |
Weakness: CWE-121, CWE-787 · Vector: CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H