Use-After-Free in BIND 9 DoH (9.20.09.20.22 / 9.21.09.21.21)
CVE-2026-3593 Published on May 20, 2026

Heap use-after-free vulnerability in BIND 9 DNS-over-HTTPS implementation
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.

Vendor Advisory NVD

Vulnerability Analysis

CVE-2026-3593 can be exploited with network access, and does not require authorization privileges or user interaction. This vulnerability is consided to have a high level of attack complexity. The potential impact of an exploit of this vulnerability is considered to have a high impact on confidentiality, with no impact on integrity, and a high impact on availability.

Attack Vector:
NETWORK
Attack Complexity:
HIGH
Privileges Required:
NONE
User Interaction:
NONE
Scope:
UNCHANGED
Confidentiality Impact:
HIGH
Integrity Impact:
NONE
Availability Impact:
HIGH

Weakness Types

What is a Dangling pointer Vulnerability?

Referencing memory after it has been freed can cause a program to crash, use unexpected values, or execute code.

CVE-2026-3593 has been classified to as a Dangling pointer vulnerability or weakness.

What is a Dangling pointer Vulnerability?

The program dereferences a pointer that contains a location for memory that was previously valid, but is no longer valid. When a program releases memory, but it maintains a pointer to that memory, then the memory might be re-allocated at a later time. If the original pointer is accessed to read or write data, then this could cause the program to read or modify data that is in use by a different function or process. Depending on how the newly-allocated memory is used, this could lead to a denial of service, information exposure, or code execution.

CVE-2026-3593 has been classified to as a Dangling pointer vulnerability or weakness.


Products Associated with CVE-2026-3593

You can be notified by email with stack.watch whenever vulnerabilities like CVE-2026-3593 are published in these products:

ISC BIND
 
Canonical Ubuntu Linux
 
Red Hat Hummingbird
 
Red Hat Enterprise Linux (RHEL)
 
Red Hat Openshift
 

Affected Versions

ISC BIND 9: Red Hat Hardened Images: Red Hat Enterprise Linux 10: Red Hat Enterprise Linux 6: Red Hat Enterprise Linux 7: Red Hat Enterprise Linux 8: Red Hat Enterprise Linux 8: Red Hat Enterprise Linux 9: Red Hat Enterprise Linux 9: Red Hat Enterprise Linux 9: Red Hat OpenShift Container Platform 4:

Exploit Probability

EPSS
1.64%
Percentile
73.36%

EPSS (Exploit Prediction Scoring System) scores estimate the probability that a vulnerability will be exploited in the wild within the next 30 days. The percentile shows you how this score compares to all other vulnerabilities.