Asterisk is an open source private branch exchange and telephony toolkit. Prior to versions 20.15.2, 21.10.2, and 22.5.2, if a SIP request is received with an Authorization header that contains a realm that wasn't in a previous 401 response's WWW-Authenticate header, or an Authorization header with an incorrect realm was received without a previous 401 response being sent, the get_authorization_header() function in res_pjsip_authenticator_digest will return a NULL. This wasn't being checked before attempting to get the digest algorithm from the header which causes a SEGV. This issue has been patched in versions 20.15.2, 21.10.2, and 22.5.2. There are no workarounds.
https://github.com/asterisk/asterisk/security/advisories/GHSA-64qc-9x89-rx5j
https://github.com/asterisk/asterisk/pull/1407
https://github.com/asterisk/asterisk/commit/02993717b08f899d4aca9888062f35dfb198584f