CVE-2022-3924: named configured to answer from stale cache may terminate unexpectedly at recursive-clients soft quota

Severity: high (CVSS 7.5 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 16.1% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2023-01-26 · updated 2026-06-17
Weakness: CWE-617

Description

This issue can affect BIND 9 resolvers with `stale-answer-enable yes;` that also make use of the option `stale-answer-client-timeout`, configured with a value greater than zero. If the resolver receives many queries that require recursion, there will be a corresponding increase in the number of clients that are waiting for recursion to complete. If there are sufficient clients already waiting when a new client query is received so that it is necessary to SERVFAIL the longest waiting client (see BIND 9 ARM `recursive-clients` limit and soft quota), then it is possible for a race to occur between providing a stale answer to this older client and sending an early timeout SERVFAIL, which may cause an assertion failure. This issue affects BIND 9 versions 9.16.12 through 9.16.36, 9.18.0 through 9.18.10, 9.19.0 through 9.19.8, and 9.16.12-S1 through 9.16.36-S1.

Affected products

ISC BIND: from 9.16.12 before 9.16.37; from 9.18.0 before 9.18.11; from 9.19.0 before 9.19.9; 9.16.12-s1, 9.16.13-s1, 9.16.14-s1, 9.16.21-s1, 9.16.32-s1, 9.16.36-s1 — fixed in 9.16.37, 9.18.11, 9.19.9

How to fix

Upgrade to a fixed version: ISC BIND 9.16.37, 9.18.11, 9.19.9. Check the vendor advisory for mitigations.

References

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