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No exploitation reportedFix available

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()

No exploitation reported by the sources we read.

  • Published2026-09-07
  • WeaknessCWE-191

Am I affected?

With a domain, we read the version its public headers and pages expose. A distribution build can carry the fix under an older number.

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.

Timeline

dates in UTC
  1. 2026-09-0715:17CVE publishedNVD

Observed activity

isMalicious corpus · updated 2026-10-23 21:37 UTC
Indicators tagged with this CVE, per day0 indicators over 7 days
Block these indicators
  • Firewall list (EDL, text): https://api.ismalicious.com/edl/cve/CVE-2026-18355?format=txt
  • CSV export: https://api.ismalicious.com/edl/cve/CVE-2026-18355?format=csv
  • TAXII collection of exploited CVEs
  • The EDL and CSV take an API key on the Pro plan.

Versions per branch

Distribution builds and vendor advisories

Packages from OSV.dev and products from the vendors' CSAF advisories.

version not verifiedVersions not verified: read as OSV.dev and the vendors publish them, not checked against each vendor's release list.

Packages

  • 389-ds-baseAlmaLinux:10all versions · fixed in 3.2.0-10.el10_2and 5 other packages
  • 389-ds-baseAlmaLinux:9all versions · fixed in 2.8.0-10.el9_8and 4 other packages
  • 389-ds-baseAlmaLinux:8all versions · fixed in 1.4.3.39-28.module_el8.10.0+4274+00f9a3f1and 5 other packages

Vendor advisories

  • CVE-2026-18355 Red Hat Product Security486 products fixed · 1 known affected

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

    redhat-ds:12/389-ds-base.src as a component of Red Hat Directory Server 12

  • RHSA-2026:79217 Red Hat Product Security13 products fixed

    Red Hat Security Advisory: redhat-ds:11 security, bug fix, and enhancement update

  • RHSA-2026:65119 Red Hat Product Security1 product fixed

    Red Hat Security Advisory: Red Hat Directory Server 13.2 container image update

  • RHSA-2026:64784 Red Hat Product Security50 products fixed

    Red Hat Security Advisory: 389-ds-base security, bug fix, and enhancement update

  • RHSA-2026:64785 Red Hat Product Security62 products fixed

    Red Hat Security Advisory: 389-ds-base security, bug fix, and enhancement update

  • RHSA-2026:64791 Red Hat Product Security42 products fixed

    Red Hat Security Advisory: 389-ds:1.4 security, bug fix, and enhancement update

12 more advisories

Full record on NVD

Fix

  1. Vendor fix Red Hat Product Security RHSA-2026:79217 · 13 productsFor details on how to apply this update, which includes the changes described in this advisory, refer to: https://access.redhat.com/articles/11258
  2. Vendor fix Red Hat Product Security RHSA-2026:65119 · 1 productThe container image provided by this update can be downloaded from the Red Hat container registry at registry.redhat.io using the "podman pull" command. For more information about the image, search the <image_name> in the Red Hat Ecosystem Catalog: https://catalog.redhat.com/software/containers/sea…
  3. Workaround from the vendor Red Hat Product Security RHSA-2026:79217 · 13 productsRed 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.

Detection

Nuclei template
none so far
ProjectDiscovery
Exploit-DB
no entry
Exploit-DB
Proof-of-concept repositories
none listed
PoC-in-GitHub

Sources

  • NVDCVE recordread 2026-10-23
  • CISA-ADPSSVC decisionnone2026-09-08
  • OpenCVESSVC decisionnone—
  • CNACVSS 3.17.5read 2026-10-23
  • CNAweakness (CWE)CWE-191read 2026-10-23
  • FIRST EPSSEPSS score0.8 %2026-10-23
  • OSVaffected packages—

Technical details

CVSS v3 Vector
CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H
Published
2026-09-07
Last Modified
2026-10-08
NVD status
Awaiting Analysis

Frequently asked questions

What is 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.

Is CVE-2026-18355 actively exploited?

Active exploitation of CVE-2026-18355 has not been confirmed. Its EPSS score was 0.8% on 2026-10-23, the estimated probability of exploitation in the next 30 days.

What is the CVSS score for CVE-2026-18355?

CVE-2026-18355 has a CVSS v3 base score of 7.5 (HIGH severity), with vector string CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H.

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