CVE-2026-18355

A heap buffer overflow flaw was found in the SASL I/O layer of 389 Directory Server (389-ds-base). In sasl_io_start_packet(), the wrapped-record length read from the wire is validated only against an upper bound. A small wire length (0, 1, or 2) produces an encrypted_buffer_count below the already-consumed encrypted_buffer_offset, causing an unsigned subtraction underflow in sasl_io_read_packet(). PR_Recv is then requested to read approximately 4 GiB into a 1024-byte heap buffer, resulting in a heap buffer overflow with attacker-controlled content. After a successful SASL bind with integrity protection (SSF > 0), a remote authenticated attacker can cause a denial of service or potentially achieve remote code execution. This flaw is distinct from CVE-2026-11774, whose fix only guards against upper-bound overflow.

• https://access.redhat.com/errata/RHSA-2026:64771
• https://access.redhat.com/errata/RHSA-2026:64776
• https://access.redhat.com/errata/RHSA-2026:64778
• https://access.redhat.com/errata/RHSA-2026:64779
• https://access.redhat.com/errata/RHSA-2026:64781
• https://access.redhat.com/errata/RHSA-2026:64783
• https://access.redhat.com/errata/RHSA-2026:64789
• https://access.redhat.com/errata/RHSA-2026:64792
• https://access.redhat.com/errata/RHSA-2026:64804
• https://access.redhat.com/security/cve/CVE-2026-18355
• https://bugzilla.redhat.com/show_bug.cgi?id=2509186