CVE-2026-3336 is a vulnerability classified under CWE-295 (Improper Certificate Validation) found in the AWS-LC cryptographic library, specifically within the PKCS7_verify() function. PKCS7 is a standard for cryptographically signing or encrypting data, often used in secure communications and software signing. The flaw arises when processing PKCS7 objects containing multiple signers: the verification process improperly validates the certificate chain for all signers except the final one. This means an attacker can craft a PKCS7 object with multiple signers and bypass the certificate chain verification for all but the last signer, effectively allowing the acceptance of forged or malicious signatures. The vulnerability does not require any authentication or user interaction and can be exploited remotely, making it accessible to unauthenticated attackers. The CVSS v3.1 score of 7.5 reflects a high severity due to the ease of exploitation (network vector, low complexity, no privileges required) and the impact on integrity, though confidentiality and availability remain unaffected. AWS customers using AWS services are not directly impacted, as AWS manages the underlying infrastructure, but any third-party or internal applications that embed AWS-LC version 1.41.0 for PKCS7 signature verification are vulnerable. The recommended mitigation is to upgrade AWS-LC to version 1.69.0, where this certificate validation logic has been corrected. No public exploits or active attacks have been reported yet, but the potential for misuse in software supply chain attacks or secure communications interception is significant.

The primary impact of CVE-2026-3336 is on the integrity of data verified using PKCS7 signatures with AWS-LC version 1.41.0. An attacker can bypass certificate chain verification for multiple signers, allowing forged or tampered signatures to be accepted as valid. This can undermine trust in signed software packages, secure messages, or any system relying on PKCS7 signatures for authentication and integrity. Organizations may face risks including unauthorized code execution, distribution of malicious updates, or acceptance of fraudulent documents. Since confidentiality and availability are not affected, the main concern is the silent compromise of data authenticity. The vulnerability's ease of exploitation and lack of required privileges increase the risk of widespread abuse, especially in environments where AWS-LC is embedded in critical cryptographic workflows. While AWS-managed services are not impacted, enterprises using AWS-LC in their own applications or third-party software must act promptly to avoid potential supply chain or communication security breaches.

To mitigate CVE-2026-3336, organizations should immediately upgrade any usage of AWS-LC to version 1.69.0 or later, where the certificate validation logic in PKCS7_verify() has been fixed. Application developers should audit their software dependencies to identify embedded versions of AWS-LC and ensure timely patching. Additionally, organizations should implement defense-in-depth by validating signatures using multiple independent libraries or tools where feasible, and monitor cryptographic verification logs for anomalies indicating potential signature forgery. For critical software distribution systems, consider adding out-of-band verification mechanisms such as hash checks or additional signature layers. Security teams should also review incident response plans to detect and respond to potential misuse of forged signatures. Finally, maintain awareness of updates from AWS and related cryptographic communities for any further advisories or exploit developments.