Asterisk's PJSIP_HEADER dialplan function can overwrite memory/cause crash when using 'update'

Vulnerability Description

Asterisk is an open source private branch exchange and telephony toolkit. In Asterisk versions 18.20.0 and prior, 20.5.0 and prior, and 21.0.0; as well as ceritifed-asterisk 18.9-cert5 and prior, the 'update' functionality of the PJSIP_HEADER dialplan function can exceed the available buffer space for storing the new value of a header. By doing so this can overwrite memory or cause a crash. This is not externally exploitable, unless dialplan is explicitly written to update a header based on data from an outside source. If the 'update' functionality is not used the vulnerability does not occur. A patch is available at commit a1ca0268254374b515fa5992f01340f7717113fa.

References

• https://github.com/asterisk/asterisk/security/advisories/GHSA-98rc-4j27-74hh
• https://github.com/asterisk/asterisk/commit/a1ca0268254374b515fa5992f01340f7717113fa
• https://lists.debian.org/debian-lts-announce/2023/12/msg00019.html