CVE-2026-33999

X server crash via compatibility-map integer underflow

Published Apr 23, 2026 · Updated Apr 23, 2026

Integer underflow in the XKB compatibility map in Red Hat Enterprise Linux allows local users to crash the X server. XkbSetCompatMap reuses space left after truncating a compat buffer without updating the valid-entry count, causing size and index calculations to underflow and read beyond the buffer. Exploitation requires access to the X11 server, either locally or through a forwarded remote session, and can interrupt the graphical service without user interaction.

CVSS severity7.8
High
EPSS probability0.38%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Integer underflow in the XKB compatibility map in Red Hat Enterprise Linux allows local users to crash the X server. XkbSetCompatMap reuses space left after truncating a compat buffer without updating the valid-entry count, causing size and index calculations to underflow and read beyond the buffer. Exploitation requires access to the X11 server, either locally or through a forwarded remote session, and can interrupt the graphical service without user interaction.

The record

CVE
CVE-2026-33999
Published
Apr 23, 2026
Updated
Apr 23, 2026
Vendor
389 Directory Server
Product
Red Hat Enterprise Linux 6
Classifications
CWE-191
Attack vector
local
Privileges
authenticated

Timeline

How it unfolded

  1. Apr 23, 2026CVE publishedPublication date reported by the CVE source.
  2. Apr 23, 2026Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Affected versions are unavailable in this record. Check the vendor advisory for version and patch details.

What conditions does exploitation require?

Attack vectorlocal
Required privilegesauthenticated

What is affected?

389 Directory Server · Red Hat Enterprise Linux 6Affected versions are unavailable in this record.
389 Directory Server · Red Hat Enterprise Linux 10Affected versions are unavailable in this record.
389 Directory Server · Red Hat Enterprise Linux 7Affected versions are unavailable in this record.
389 Directory Server · Red Hat Enterprise Linux 9Affected versions are unavailable in this record.
389 Directory Server · Red Hat Enterprise Linux 8Affected versions are unavailable in this record.

Published CVSS scores

7.8Red Hat, Inc.CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
7.8redhat-SADPCVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectorlocal
Privilegesauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-191Integer Underflow (Wrap or Wraparound)

Public exploit references

No public exploit references are available in this record.

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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