CVE-2026-18355: 389-ds-base: 389-ds-base: heap buffer overflow via sasl wrapped-record length lower-bound underflow in sasl_io_start_packet()

Is it exploited?

Not on CISA's list. CISA has not added it to the Known Exploited Vulnerabilities catalog as of 29 Oct 2026. If CISA adds it, this page shows it as known exploited.

How likely is exploitation in the next 30 days?

0.8%

EPSS score, percentile 57.7 of all scored records. A probability estimated by FIRST, not a report of exploitation.

How severe?

7.5 High

CVSS v3.1 base score, given by the CNA

What should I do?

CISA has set no required action, because the vulnerability is not in KEV.

Advisories and patches (12)

Which versions are affected?

Unaffected 8060020260908152739.0ca98e7e; 8080020260903102346.f969626e; 8100020260904171440.37ed7c03; 9020020260903155914.1674d574; 9040020260903102623.1674d574; 0:3.2.0-10.el10_2; and 14 more

Versions by product

Source: CISA KEV 2026.10.29, as of 29 Oct 2026; FIRST EPSS, as of 29 Oct 2026; CVE List, as of 29 Oct 2026. About the data.

What to do

Workaround (from the CVE record)

Red Hat has investigated whether a possible mitigation exists for this issue, and has not been able to identify a practical example. Please update the affected package as soon as possible.

Advisories and patches

• RHSA-2026:64771 (Vendor advisory)
• RHSA-2026:64776 (Vendor advisory)
• RHSA-2026:64778 (Vendor advisory)
• RHSA-2026:64779 (Vendor advisory)
• RHSA-2026:64780 (Vendor advisory)
• RHSA-2026:64781 (Vendor advisory)
• RHSA-2026:64783 (Vendor advisory)
• RHSA-2026:64784 (Vendor advisory)
• RHSA-2026:64785 (Vendor advisory)
• RHSA-2026:64789 (Vendor advisory)
• RHSA-2026:64790 (Vendor advisory)
• RHSA-2026:64791 (Vendor advisory)

This summary is based on the CVE record as of 29 Oct 2026. Check the vendor's advisory before you act: affected versions and fixes can change.

Affected products and versions

As listed in the CVE record.

Versions not listed are: affected.

Versions not listed are: affected.

Versions not listed are: affected.

Versions not listed are: affected.

Versions not listed are: affected.

Versions not listed are: affected.

Versions not listed are: affected.

Versions not listed are: affected.

Versions not listed are: affected.

Versions not listed are: affected.

Versions not listed are: affected.

Versions not listed are: affected.

Versions not listed are: affected.

Versions not listed are: affected.

Versions not listed are: affected.

Versions not listed are: affected.

Versions not listed are: affected.

Versions not listed are: affected.

Versions not listed are: affected.

Versions not listed are: affected.

Versions the record lists as unaffected: 8060020260908152739.0ca98e7e, 8080020260903102346.f969626e, 8100020260904171440.37ed7c03, 9020020260903155914.1674d574, 9040020260903102623.1674d574, 0:3.2.0-10.el10_2, 0:3.0.6-21.el10_0, 0:1.3.11.1-15.el7_9.

Source: CVE List, as of 29 Oct 2026. About the data.

About this vulnerability

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()…

Summary: CVE record, as of 29 Oct 2026.

• CISA has not added CVE-2026-18355 to its Known Exploited Vulnerabilities (KEV) catalog, as of 29 Oct 2026.
• The CVE record was published on 7 Sep 2026.
• The CVE record carries a CVSS v3.1 base score of 7.5 (High), given by its CNA.
• FIRST's EPSS model puts the probability of exploitation in the next 30 days at 0.8% (percentile 57.7), as of 29 Oct 2026. EPSS is a statistical estimate, not a report of exploitation.
• CISA's SSVC assessment in the CVE record: exploitation none, automatable no, technical impact total.
• The credits in the CVE record name Anthropic (Claude) as finder.

Source: CISA KEV 2026.10.29, as of 29 Oct 2026; CVE List, as of 29 Oct 2026; FIRST EPSS, as of 29 Oct 2026. About the data.

Description

389-ds-base: 389-ds-base: heap buffer overflow via sasl wrapped-record length lower-bound underflow in sasl_io_start_packet()

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.

Source: CVE List, as of 29 Oct 2026. About the data.

Timeline

Known exploited Red Hat vulnerabilities

• CVE-2015-3246: Red Hat Libuser Race Condition Vulnerability (added 26 Aug 2026)
• CVE-2015-5287: Red Hat Automatic Bug Reporting Tool Privilege Escalation Vulnerability (added 26 Aug 2026)
• CVE-2018-14667: Red Hat JBoss RichFaces Framework Expression Language Injection Vulnerability (added 28 Sep 2023)
• CVE-2021-3560: Red Hat Polkit Incorrect Authorization Vulnerability (added 12 May 2023)
• CVE-2021-4034: Red Hat Polkit Out-of-Bounds Read and Write Vulnerability (added 27 Jun 2022)