Red Hat Directory Server/Enterprise Linux up to 388 SASL I/O Layer sasl_io_start_packet heap-based overflow

Summaryinfo

A vulnerability has been found in Red Hat Directory Server and Enterprise Linux up to 388 and classified as very critical. This affects the function sasl_io_start_packet of the component SASL IO Layer. The manipulation leads to heap-based overflow. This vulnerability is referenced as CVE-2026-18355. Remote exploitation of the attack is possible. No exploit is available.

Detailsinfo

A vulnerability was found in Red Hat Directory Server and Enterprise Linux up to 388 and classified as very critical. This issue affects the function sasl_io_start_packet of the component SASL IO Layer. The manipulation with an unknown input leads to a heap-based overflow vulnerability. Using CWE to declare the problem leads to CWE-122. A heap overflow condition is a buffer overflow, where the buffer that can be overwritten is allocated in the heap portion of memory, generally meaning that the buffer was allocated using a routine such as malloc(). Impacted is confidentiality, integrity, and availability. The summary by CVE is:

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.

The advisory is shared at access.redhat.com. The identification of this vulnerability is CVE-2026-18355 since 07/30/2026. The exploitation is known to be easy. The attack may be initiated remotely. Technical details are known, but no exploit is available. The price for an exploit might be around USD $5k-$25k at the moment (estimation calculated on 09/07/2026).

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

Type

• Directory Service Software

Vendor

• Red Hat

Name

• Directory Server
• Enterprise Linux

Version

• 388

License

• open-source

Website

• Vendor: https://www.redhat.com/

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