Executive brief
OpenSSL is a widely used security library that provides encryption for internet communications and data storage. A flaw in how it handles specific encryption types on modern Intel-compatible processors could allow an attacker to cause an application to crash. This would result in a service outage, though it does not appear to risk the theft of sensitive data.
Technical details
An out-of-bounds read vulnerability exists in the OpenSSL AES-CFB128 implementation for x86-64 systems supporting AVX-512 and VAES instructions. The root cause is the use of unmasked 'vmovdqu8' instructions in the pre-processing code of 'ossl_aes_cfb128_vaes_enc' and 'ossl_aes_cfb128_vaes_dec', which unconditionally load 16 bytes even when processing partial blocks. An attacker can trigger a read of up to 15 bytes beyond the input buffer; if this buffer ends at a memory page boundary and the adjacent page is unmapped, the application will crash (Denial of Service). This issue does not affect TLS/DTLS as they do not use CFB mode. Users should upgrade to OpenSSL 3.6.2.
Affected products
- OpenSSL OpenSSL 3.6.0, 3.6.1
Timeline
- 2026-01-06: disclosed: Reported by Stanislav Fort and Pavel Kohout (Aisle Research)
- 2026-03-10: disclosed: Independently reported by Alex Gaynor (Anthropic)
- 2026-04-07: advisory
- 2026-04-07: patched