wolfSSL up to 5.9.1 EnvelopedData timing discrepancy

Summaryinfo

A vulnerability classified as problematic was found in wolfSSL up to 5.9.1. Affected by this issue is some unknown functionality of the component EnvelopedData Handler. The manipulation results in timing discrepancy. This vulnerability was named CVE-2026-6291. The attack may be performed from remote. There is no available exploit.

Detailsinfo

A vulnerability classified as problematic has been found in wolfSSL up to 5.9.1. Affected is an unknown function of the component EnvelopedData Handler. The manipulation with an unknown input leads to a timing discrepancy vulnerability. CWE is classifying the issue as CWE-208. Two separate operations in a product require different amounts of time to complete, in a way that is observable to an actor and reveals security-relevant information about the state of the product, such as whether a particular operation was successful or not. This is going to have an impact on confidentiality. CVE summarizes:

Bleichenbacher padding oracle in PKCS#7 KTRI decryption. When decrypting PKCS#7 EnvelopedData using RSA PKCS#1 v1.5 key transport, wolfSSL returned distinguishable error codes depending on whether RSA padding validation failed versus whether the decrypted content was malformed. An attacker able to submit crafted EnvelopedData messages and observe error responses could use this as a padding oracle to incrementally recover the encrypted Content Encryption Key (CEK). The fix generates a deterministic pseudo-random fake CEK on padding failure (via HMAC-SHA256) and proceeds with decryption identically, using constant-time operations throughout, so that all failure paths produce the same error regardless of padding validity.

The advisory is shared for download at github.com. This vulnerability is traded as CVE-2026-6291 since 04/14/2026. The exploitability is told to be easy. It is possible to launch the attack remotely. There are neither technical details nor an exploit publicly available. The MITRE ATT&CK project declares the attack technique as T1592.

There is no information about possible countermeasures known. It may be suggested to replace the affected object with an alternative product.

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Productinfo

Name

• wolfSSL

Version

• 5.9.0
• 5.9.1

License

• open-source

Website

• Product: https://github.com/wolfSSL/wolfssl/

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