CVE-2013-3900

Microsoft's WinVerifyTrust function improperly validates Windows Authenticode signatures on portable executable (PE) files, allowing crafted modifications to a signed binary — such as altered sections or checksum-table manipulation — to still pass signature verification. An attacker who tampers with a legitimately signed executable can distribute modified files that Windows and dependent security controls treat as authentic, gaining the trust of a valid digital signature and, ultimately, remote code execution in contexts that rely on signature checks. Any Microsoft Windows platform performing Authenticode verification through WinVerifyTrust is affected; the source data does not list specific Windows version ranges, but because WinVerifyTrust is core Windows functionality the exposure is very broad. The flaw was added to CISA's Known Exploited Vulnerabilities catalog on 2022-01-10, indicating confirmed in-the-wild exploitation, and EPSS puts its 30-day exploitation probability at about 44.6% (99th percentile), though no public PoC is known.

What to do: Apply Microsoft's updates for CVE-2013-3900 across all Windows systems per vendor instructions, as required for CISA KEV entries. Where supported, enable Microsoft's stricter certificate padding check (EnableCertPaddingCheck) per Microsoft guidance to harden signature verification against this bypass. Prioritize patching endpoints and servers that execute or validate downloaded, emailed, or otherwise externally sourced signed binaries, given confirmed exploitation and high EPSS.