CVE-2026-3593
Use-After-Free in BIND 9 DNS-over-HTTPS Implementation
Publication date: 2026-05-20
Last updated on: 2026-05-20
Assigner: Internet Systems Consortium (ISC)
Description
Description
CVSS Scores
EPSS Scores
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Meta Information
Affected Vendors & Products
| Vendor | Product | Version / Range |
|---|---|---|
| isc | bind | 9.20.0 |
| isc | bind | 9.20.22 |
| isc | bind | 9.21.0 |
| isc | bind | 9.21.21 |
| isc | bind | 9.20.9-s1 |
| isc | bind | 9.20.22-s1 |
Helpful Resources
Exploitability
| CWE ID | Description |
|---|---|
| CWE-416 | 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 Any operations using the original pointer are no longer valid because the memory "belongs" to the code that operates on the new pointer. |
Attack-Flow Graph
AI Powered Q&A
Can you explain this vulnerability to me?
CVE-2026-3593 is a high-severity use-after-free vulnerability found in the DNS-over-HTTPS implementation of BIND 9. This flaw allows specially crafted HTTP/2 traffic to cause memory corruption in both authoritative DNS servers and resolvers that run vulnerable versions of BIND 9.
The affected versions include BIND 9.20.0 through 9.20.22, 9.21.0 through 9.21.21, and the Supported Preview Editions 9.20.9-S1 through 9.20.22-S1. Versions 9.18.0 through 9.18.48 and 9.18.11-S1 through 9.18.48-S1 are not affected.
How does this vulnerability affect compliance with common standards and regulations (like GDPR, HIPAA)?:
The provided information does not specify any direct impact of this vulnerability on compliance with common standards and regulations such as GDPR or HIPAA.
How can this vulnerability impact me? :
This vulnerability can lead to memory corruption on affected DNS servers and resolvers, which may cause crashes or unpredictable behavior. Because it is a use-after-free flaw triggered by crafted HTTP/2 traffic, it could potentially be exploited to disrupt DNS services or cause denial of service.
The CVSS v3.1 base score is 7.4, indicating a high severity impact with network attack vector, high attack complexity, no privileges required, no user interaction, and high impact on confidentiality and availability.
What immediate steps should I take to mitigate this vulnerability?
To mitigate the CVE-2026-3593 vulnerability, you should either disable DNS-over-HTTPS or upgrade your BIND 9 installation to a patched release.
- Upgrade to BIND 9.20.23, 9.21.22, or 9.20.23-S1, which contain fixes for this vulnerability.
- If upgrading is not immediately possible, disable the DNS-over-HTTPS feature to prevent exploitation.