Vulnerability in Wolfssl
CVE-2026-6291
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.
Published · last modified .
CVSS v3 metric
CVSS v3 base score 6.5 (Medium). Vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:N.
EPSS exploit prediction
EPSS: 0.002 (13.9th percentile), scored .
Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 14th percentile — 13.9% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.
EPSS over last 30 days · oldest: 0.002 · newest: 0.002 · change: 0.000
Affected products
- Wolfssl — versions 3.9.10
Weakness classification (CWE)
References
- github.com/wolfSSL/wolfssl/pull/10203 (patch, Issue Tracking)
- www.wolfssl.com/docs/security-vulnerabilities/ (Vendor Advisory)
Frequently asked questions
- What is CVE-2026-6291?
- CVE-2026-6291 is a medium-severity vulnerability in Wolfssl, classified under CWE-208. CVSS score: 6.5/10. Published 2026-06-25.
- How severe is CVE-2026-6291?
- Medium severity. CVSS v3 base score is 6.5 out of 10.