Bug 2456928 (CVE-2026-39853)

Summary: CVE-2026-39853 osslsigncode: stack buffer overflow via unbounded digest copy during signature verification
Product: [Other] Security Response Reporter: OSIDB Bzimport <bzimport>
Component: vulnerabilityAssignee: Product Security <prodsec-ir-bot>
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Version: unspecifiedKeywords: Security
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OS: Linux   
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A flaw was found in osslsigncode. A stack buffer overflow vulnerability can occur during the verification of PKCS#7 signatures in various file types. An attacker can exploit this flaw by crafting a malicious signed file with an oversized digest. When this file is verified by a user, it can lead to the execution of arbitrary code or a denial of service.
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Description OSIDB Bzimport 2026-04-09 16:01:36 UTC 
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.