AWS-LC CVE-2026-3336

Exploitation requires that the target application process PKCS7 objects containing MULTIPLE signers and rely on AWS-LC PKCS7_verify() to make a trust decision - the flaw only skips chain verification for all signers except the final one, so single-signer PKCS7 verification is not affected. No authentication, privileges, or user interaction are needed (PR:N/UI:N), and the attacker only needs to deliver a crafted multi-signer PKCS7 structure to the verifying application. Limiting factors: applications that never use multi-signer PKCS7 verification, or that only verify single-signer messages, are not exploitable; the issue is fixed in AWS-LC 1.69.0; and impact is integrity-only (no data disclosure or denial of service).

Signals are largely consistent and point to a moderate, integrity-focused issue rather than an urgent crisis. The CVSS 4.0 vector (AV:N/AC:L/AT:N/PR:N/UI:N) with VI:H and VC:N/VA:N correctly frames this as a network-reachable, no-privilege, no-interaction integrity bypass with no confidentiality or availability impact, consistent with the description of an unauthenticated certificate-validation bypass. The vendor score of 8.7 is driven by the unauthenticated network reach; however EPSS is very low (0.03%, 10th percentile), it is not on CISA KEV, and no POC is referenced, so widespread opportunistic exploitation is unlikely. Real-world risk is conditional: it only matters for applications that actually call PKCS7_verify() on multi-signer PKCS7 objects and make trust decisions on the result - a meaningful but not universal code path. Key caveat: exploitability depends entirely on whether the consuming application uses multi-signer PKCS7 verification, which the CVE metadata cannot confirm for any given deployment.

An attacker crafts a PKCS7 signed message containing multiple signers where an earlier signer uses an untrusted or invalid certificate while the final signer is benign or valid; an application using a pre-1.69.0 AWS-LC PKCS7_verify() accepts the whole structure as verified, allowing the attacker to spoof a trusted signer on signed content or updates. No public POC is referenced, but the network attack vector and low complexity (AC:L, no privileges, no user interaction) make exploitation straightforward against any vulnerable verification path.