Executive Summary

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.

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Compliance Impact

The provided information does not specify any direct impact of this vulnerability on compliance with common standards and regulations such as GDPR or HIPAA.

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Impact Analysis

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.

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Mitigation Strategies

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.

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Detection Guidance

This vulnerability affects specific versions of BIND 9 with DNS-over-HTTPS enabled. Detection involves identifying if your system is running a vulnerable BIND 9 version and monitoring for suspicious or crafted HTTP/2 traffic targeting DNS-over-HTTPS.

To detect vulnerable versions, you can check the installed BIND version with commands like:

• named -v
• named -V

To monitor network traffic for suspicious HTTP/2 requests that might exploit the vulnerability, you can use packet capture tools such as tcpdump or Wireshark filtering for HTTP/2 traffic on port 443 or the port used for DNS-over-HTTPS:

• tcpdump -i <interface> 'tcp port 443 and (((ip[2:2] - ((ip[0]&0xf)<<2)) - ((tcp[12]&0xf0)>>2)) != 0)'
• Use Wireshark with a filter for http2 or tls.handshake.type == 1 to inspect HTTP/2 traffic.

Additionally, reviewing BIND logs for crashes or memory corruption events related to DNS-over-HTTPS requests can help identify exploitation attempts.

Since no active exploits have been reported, the best detection is ensuring your BIND version is patched or DNS-over-HTTPS is disabled.

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