BIND 9: Improper Filtering of Special Elements
CVE-2026-11331 is a high-severity improper filtering of special elements vulnerability in BIND 9 from ISC, with a CVSS 3.1 base score of 7.5 out of 10. It can be exploited remotely over the network by an unauthenticated attacker, without any action from a user. Affected BIND 9 versions: 9.16.0 through 9.18.50; 9.20.0 through 9.20.24; 9.21.0 through 9.21.23, and others listed below. The record does not name a fixed version, so check the vendor advisory. There is no confirmed exploitation so far. EPSS estimates a 0.43% chance of exploitation within 30 days, which is low compared with other CVEs.
High severity with no evidence of exploitation so far.
What to do
- Check which version of BIND 9 you run against the affected versions below, and install the vendor's latest release.
- Read the advisory on kb.isc.org for workarounds and exact fixed builds.
- Until you can update, restrict network access to the affected service so it is not reachable from untrusted networks.
Affected products and versions
| Vendor | Product | Affected versions | Fixed in |
|---|---|---|---|
| ISC | BIND 9 | 9.16.0 through 9.18.50; 9.20.0 through 9.20.24; 9.21.0 through 9.21.23; 9.16.8-S1 through 9.18.50-S1; 9.20.9-S1 through 9.20.24-S1 | Not stated |
| ISC | Bind | 9.16.8 through 9.18.50; 9.18.0 through 9.18.50; 9.20.0 through 9.20.24; 9.20.9 through 9.20.24; 9.21.0 through 9.21.23 | Not stated |
Version data comes from the organisation that assigned the CVE. Confirm against the vendor advisory before deciding you are unaffected.
How the severity score breaks down
- Attack vector
- NetworkCan be exploited remotely over a network, including the internet.
- Attack complexity
- LowNo special conditions are needed; the attack works reliably.
- Privileges required
- NoneNo account or login is needed.
- User interaction
- NoneNo action by a victim is required.
- Scope
- UnchangedImpact stays within the vulnerable component.
- Confidentiality
- HighAll data handled by the component can be read.
- Integrity
- NoneNothing can be modified.
- Availability
- NoneAvailability is not affected.
Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N. Scored by CNA (isc.org).
Official description
An attacker who knows (or guesses) that a resolver uses RPZ with wildcard CNAME policies can craft query names long enough to trigger a NAMETOOLONG error condition during RPZ processing. This is not handled correctly and may lead to defeating the RPZ rule. It also may lead to an unexpected exit of the BIND 9 software. This issue affects BIND 9 versions 9.16.0 through 9.18.50, 9.20.0 through 9.20.24, 9.21.0 through 9.21.23, 9.16.8-S1 through 9.18.50-S1, and 9.20.9-S1 through 9.20.24-S1.
Source: the CVE record as published by its numbering authority, via NVD and CVE.org.
The underlying weakness: Improper Filtering of Special Elements
The product receives data from an upstream component, but it does not filter or incorrectly filters special elements before sending it to a downstream component.
More Improper Filtering of Special Elements vulnerabilities (CWE-790)
Timeline
- CVE record published.
- CISA published its SSVC assessment (exploitation: none, automatable: yes, technical impact: partial).
- Record last changed materially (score, affected products, status or references).
References
Advisories
Other references
Other vulnerabilities in BIND 9
- 7.5 High severity
- 7.5 High severity
- 8.1 High severity
- 7.5 High severity
- 7.5 High severity
- 7.5 High severity
Recent Improper Filtering of Special Elements vulnerabilities
- 7.5 High severity
- 7.5 High severity
- 8.8 High severity
- 9.8 Critical severity
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