BIND 9: Use After Free
CVE-2026-3593 is a critical-severity use after free vulnerability in BIND 9 from ISC, with a CVSS 3.1 base score of 9.8 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: 9.20.0 through 9.20.22; 9.21.0 through 9.21.21; 9.20.9-S1 through 9.20.22-S1. The record does not name a fixed version, so check the vendor advisory. There is no confirmed exploitation so far. EPSS estimates a 1.54% chance of exploitation within 30 days, higher than 75% of scored CVEs.
Critical severity: a successful attack would have severe impact.
What to do
- Update Bind to 9.20.23 or 9.21.22, whichever matches your release line, or a later version.
- 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 | 9.20.0 through 9.20.22; 9.21.0 through 9.21.21; 9.20.9-S1 through 9.20.22-S1 | Not stated |
| Red Hat | Red Hat Hardened Images | Not specified in the record | Not stated |
| Red Hat | Red Hat Enterprise Linux 10 | Not specified in the record | Not stated |
| Red Hat | Red Hat Enterprise Linux 6 | Not specified in the record | Not stated |
| Red Hat | Red Hat Enterprise Linux 7 | Not specified in the record | Not stated |
| Red Hat | Red Hat Enterprise Linux 8 | Not specified in the record | Not stated |
| Red Hat | Red Hat Enterprise Linux 9 | Not specified in the record | Not stated |
| Red Hat | Red Hat OpenShift Container Platform 4 | Not specified in the record | Not stated |
| ISC | Bind | 9.20.0 up to, but not including, 9.20.23; 9.21.0 up to, but not including, 9.21.22 | 9.20.23, 9.21.22 |
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
- HighData or code can be modified at will.
- Availability
- HighThe component can be taken down completely.
Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H. Scored by NVD.
| Scoring system | Score | Severity | Scored by |
|---|---|---|---|
| CVSS 3.1 | 7.4 | High | CNA (isc.org) |
| CVSS 3.1 | 9.8 | Critical | NVD |
| CVSS 3.1 | 7.4 | High | CNA |
Official description
A use-after-free vulnerability exists within the DNS-over-HTTPS implementation. This issue affects BIND 9 versions 9.20.0 through 9.20.22, 9.21.0 through 9.21.21, and 9.20.9-S1 through 9.20.22-S1. BIND 9 versions 9.18.0 through 9.18.48 and 9.18.11-S1 through 9.18.48-S1 are NOT affected.
Source: the CVE record as published by its numbering authority, via NVD and CVE.org.
The underlying weakness: Use After Free
The product reuses or references memory after it has been freed. At some point afterward, the memory may be allocated again and saved in another pointer, while the original pointer references a location somewhere within the new allocation. Any operations using the original pointer are no longer valid because the memory belongs to the code that operates on the new pointer.
How developers prevent this class of flaw
- Choose a language that provides automatic memory management.
- When freeing pointers, be sure to set them to NULL once they are freed. However, the utilization of multiple or complex data structures may lower the usefulness of this strategy.
Timeline
- CVE record published.
- CISA published its SSVC assessment (exploitation: none, automatable: no, technical impact: partial).
- Record last changed materially (score, affected products, status or references).
References
Advisories
Patches and release notes
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 Use After Free vulnerabilities
- 8.8 High severity
- 8.8 High severity
- 8.8 High severity
- 8.8 High severity
- 8.8 High severity
- 8.8 High severity
Spotted an error? Tell us.