CVE-1999-0526X11 Vulnerability
An X server's access control is disabled (e.g.
Published Jul 1, 1997 · Updated Apr 15, 2026
Key Facts
Patch immediately- CVE-1999-0526 is a critical-severity vulnerability (CVSS 10.0 v2) affecting X11 (X.org).
- It is exploited in the wild, listed in Industry KEV feed since Feb 27, 2025. Public exploit code is available.
- EPSS estimates a 21% probability of exploitation in the next 30 days.
- No fixed version is listed yet; check the vendor advisory for mitigations.
- Brandefense priority: patch immediately, because it is listed as exploited in the wild.
Scores
CVSS v2
10.0
AV:N/AC:L/Au:N/C:C/I:C/A:C
EPSS (30-day exploit likelihood)
21%
Higher than 97.5% of all scored CVEs
Exploit maturity
Weaponized
ATLAS score
47/100
Publication score, see How it works
Exploitation Verdict
KEV listed
Feb 27, 2025
Federal due date
None
No federal due date
Ransomware use
Not reported
Attributed actors
None named
Exploit & Defence Guidance
Exploit maturity
Weaponized
Public exploit code
1
Proof-of-concept links
In-the-wild evidence
3
Reports of active use
Description
An X server's access control is disabled (e.g. through an "xhost +" command) and allows anyone to connect to the server.
Known-Exploited Catalog Listings
| Catalog | Added | Remediation due | Ransomware use |
|---|---|---|---|
| Industry KEV feed | Feb 27, 2025 | n/a | Not reported |
Affected Products
1 affected entries in total| Product | Affected versions | Fixed in |
|---|---|---|
| X11X.org | 7.1_1.1.0 | n/a |
Timeline
Publicly disclosed
Jul 1, 1997
Added to Industry KEV feed
Feb 27, 2025
Last updated
Apr 15, 2026
References
- exploitVulnCheck exploitation report
- exploitVulnCheck exploitation report
- exploitMSF x11_keyboard_exec.rb
- exploitVulnCheck exploitation report
- otherVU#704969
FAQ
Common Questions.
An X server's access control is disabled (e.g.
Affected: X11 (X.org) versions 7.1_1.1.0. The full list is in the CVE brief.
It is exploited in the wild, listed in Industry KEV feed since Feb 27, 2025.
No, it is not currently listed in the CISA Known Exploited Vulnerabilities catalog.
Public exploit code is available.
No fixed version is listed yet; check the vendor advisory for mitigations.
Brandefense priority: patch immediately, because it is listed as exploited in the wild.
Is CVE-1999-0526 On Your Attack Surface?
Brandefense matches it against the products discovered on your perimeter and opens a finding the day a CVE like this is listed.
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