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Response snapshot Nov 4, 2026, 23:06 UTC

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VulnerabilityCVE-2026-18355

A heap buffer overflow flaw was found in the SASL I/O layer of 389 Directory Server (389-ds-base).

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.

At a glance

Exploited
Not known
Severity
7.5 High (CVSS 3.1)
Chance of exploitation
Not estimated
Sources
1 source

What to do

Check the vendor advisory for affected versions and fixes.

Read NVD CVE-2026-18355 (opens a new tab)

What happened

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.

Scores and how they were measured

CVSS base severity

7.5

Version 3.1As of

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

Measurement source (opens a new tab)

How bad it is if exploited. Not a prediction of exploitation or proof you are exposed.

EPSS probability

Not available

A model's estimate of exploitation in the next 30 days, not certainty or your own risk.

Sources

  1. Primary source

    NVD CVE-2026-18355 (opens a new tab)

    NVD record: description, CVSS (the CNA score is preferred), affected products, and publication date. Not evidence of exploitation.

    Published Checked

  2. Primary source

    NVD CVE API 2.0 (opens a new tab)

    The NVD API page that supplied this CVE record.

    Published Date not suppliedChecked

  3. Primary source

    NVD CVE API 2.0 (opens a new tab)

    The NVD API page that supplied this CVE record.

    Published Date not suppliedChecked

Cite this record

For factual claims, cite the primary sources above; cite KEVWire for its compilation, dates, and classifications.

APA

KEVWire. (2026, November 4). A heap buffer overflow flaw was found in the SASL I/O layer of 389 Directory Server (389-ds-base). (CVE-2026-18355). https://kevwire.com/record/CVE-2026-18355

MLA

"A heap buffer overflow flaw was found in the SASL I/O layer of 389 Directory Server (389-ds-base). (CVE-2026-18355)." KEVWire, 4 Nov. 2026, kevwire.com/record/CVE-2026-18355.

Chicago

KEVWire. "A heap buffer overflow flaw was found in the SASL I/O layer of 389 Directory Server (389-ds-base). (CVE-2026-18355)." Last modified November 4, 2026. https://kevwire.com/record/CVE-2026-18355.

Evidence summary (plain text)

A heap buffer overflow flaw was found in the SASL I/O layer of 389 Directory Server (389-ds-base). (Sep 7, 2026).
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.
CVSS 7.5 (version 3.1; evidence as of Nov 4, 2026; https://nvd.nist.gov/vuln/detail/CVE-2026-18355).
Sources:
NVD CVE-2026-18355: https://nvd.nist.gov/vuln/detail/CVE-2026-18355
NVD CVE API 2.0: https://services.nvd.nist.gov/rest/json/cves/2.0?lastModStartDate=2026-11-04T21:26:17.946Z&lastModEndDate=2026-11-04T23:00:56.752Z&resultsPerPage=500&startIndex=0
NVD CVE API 2.0: https://services.nvd.nist.gov/rest/json/cves/2.0?lastModStartDate=2026-11-04T20:50:59.749Z&lastModEndDate=2026-11-04T22:25:56.739Z&resultsPerPage=500&startIndex=0
Record ID: CVE-2026-18355.
Record origin: Ingested record.
AI evidence: Not assessed.
Known exploitation: Not assessed.
Zero-day status: Not assessed. KEV membership alone does not establish zero-day status.
About this data

This record was ingested from a data source. Retrieved: Nov 4, 2026, 23:00 UTC. Ingestion is not an independent editorial investigation.

NVD status: Awaiting Analysis. Publication in the NVD is not evidence of exploitation.

A CISA KEV listing documents known exploitation, not necessarily a zero-day; absence from the catalog does not prove a vulnerability has never been exploited.

Technology tags indicate possible relevance, not verified exposure. Confirm the affected product, version, and configuration against your own inventory; KEVWire does not scan your systems.

A personal reading checklist on this device, not verified remediation.

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Record details

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