CVE-2024-42491: A malformed Contact or Record-Route URI in an incoming SIP request can cause Asterisk to crash when res_resolver_unbound is used

Severity: medium (CVSS 5.7 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.6% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2024-09-05 · updated 2026-06-17
Weakness: CWE-252

Description

Asterisk is an open-source private branch exchange (PBX). Prior to versions 18.24.3, 20.9.3, and 21.4.3 of Asterisk and versions 18.9-cert12 and 20.7-cert2 of certified-asterisk, if Asterisk attempts to send a SIP request to a URI whose host portion starts with `.1` or `[.1]`, and res_resolver_unbound is loaded, Asterisk will crash with a SEGV. To receive a patch, users should upgrade to one of the following versions: 18.24.3, 20.9.3, 21.4.3, certified-18.9-cert12, certified-20.7-cert2. Two workarounds are available. Disable res_resolver_unbound by setting `noload = res_resolver_unbound.so` in modules.conf, or set `rewrite_contact = yes` on all PJSIP endpoints. NOTE: This may not be appropriate for all Asterisk configurations.

Affected products

asterisk: before 18.24.3; from 20.0.0 before 20.9.3; from 21.0.0 through 21.4.3 — fixed in 18.24.3, 20.9.3
Sangoma Certified Asterisk: before 18.9; 18.9, 18.9-cert1, 18.9-cert1-rc1, 18.9-cert10, 18.9-cert11, 18.9-cert2 (+13) — fixed in 18.9

How to fix

Upgrade to a fixed version: asterisk 18.24.3, 20.9.3; Sangoma Certified Asterisk 18.9. Check the vendor advisory for mitigations.

References

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