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.

Scoring

Severity

HIGH

CVSS base score

7.5

CVSS vector

CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H

EPSS probability

0.84%

CWE

CWE-191

Published

2026-09-07

Last modified

2026-09-09

Affected products

• Red Hat Red Hat Enterprise Linux 7 Extended Lifecycle Support
• Red Hat Red Hat Directory Server 11.7 E4S for RHEL 8
• Red Hat Red Hat Directory Server 12.2 E4S for RHEL 9
• Red Hat Red Hat Enterprise Linux 8.4 Advanced Mission Critical Update Support
• Red Hat Red Hat Enterprise Linux 8.4 Extended Update Support Long-Life Add-On
• Red Hat Red Hat Enterprise Linux 8.8 Telecommunications Update Service
• Red Hat Red Hat Enterprise Linux 8.8 Update Services for SAP Solutions
• Red Hat Red Hat Enterprise Linux 9.2 Update Services for SAP Solutions

Weakness type

• CWE-191

Related vulnerabilities

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• CVE-2026-77488 — Microsoft SQL Server Information Disclosure Vulnerability
• CVE-2026-71352 — Windows Remote Access Connection Manager Remote Code Execution Vulnerability
• CVE-2026-69824 — Microsoft Standard XPS Remote Code Execution Vulnerability
• CVE-2026-69687 — Windows USB Audio Class driver (usbaudio.sys) Elevation of Privilege Vulnerability
• CVE-2026-69421 — Windows Kernel-Mode Driver Elevation of Privilege Vulnerability

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