CVE-2025-15467

OpenSSL 3.0, 3.3, 3.4, 3.5 and 3.6 contain a stack-based out-of-bounds write (CWE-787/CWE-120) in their CMS parser: when decoding CMS AuthEnvelopedData or EnvelopedData parameters for AEAD ciphers such as AES-GCM, the ASN.1-encoded IV is copied into a fixed-size stack buffer without checking its length. An attacker triggers it by sending a crafted CMS/PKCS#7 message (e.g., an S/MIME enveloped message) with an oversized IV to any application that parses it; the overflow occurs before authentication or tag verification, so no valid key material is required, though the target must process attacker-supplied content (CVSS UI:R). Successful exploitation causes a crash (denial of service) and, depending on platform and toolchain mitigations, potentially remote code execution. Only applications and services parsing untrusted CMS content with the listed OpenSSL 3.x series are affected; OpenSSL 1.1.1, 1.0.2 and the FIPS modules in 3.0/3.3/3.4/3.5/3.6 are not affected, since the CMS implementation lies outside the FIPS module boundary. There is no confirmed in-the-wild exploitation or KEV listing yet, but a public proof-of-concept exists and EPSS assigns a 48.2% (99th-percentile) probability of exploitation within 30 days.

What to do: Upgrade all OpenSSL 3.0/3.3/3.4/3.5/3.6 deployments to the patched releases referenced in the OpenSSL security advisory, and rebuild or update products, distributions and appliances that bundle affected 3.x libraries. Until patched, mitigate by avoiding or restricting parsing of untrusted CMS/PKCS#7 (Auth)EnvelopedData with AEAD ciphers (e.g., disable or filter S/MIME enveloped-mail processing for external senders) and inventory which services accept CMS content. Note that FIPS-module-only deployments are unaffected because CMS parsing is outside the module boundary.