Sending a malformed Via header to OpenSIPS triggers a segmentation fault when the function calc_tag_suffix is called. A specially crafted Via header which is deemed correct by the parser, will pass uninitialized strings to the function MD5StringArray which leads to the crash. The following is a payload that demonstrates this issue:

OPTIONS sip:127.0.0.1 SIP/2.0<CRLF>
Via: SIP/2.0/\x16UD~PTo :::]<LF>
Via: SIP/2.0/UD~PToD~PTo :::]<LF>
\x16ia: SIP/2.0/UD~PTo ::trA><CRLF>
To:. <sv:>;tga\x91o5;tga=0fe

Impact

Abuse of this vulnerability leads to Denial of Service due to a crash. Since the uninitialized string points to memory location 0x0, no further exploitation appears to be possible. No special network privileges are required to perform this attack, as long as the OpenSIPS configuration makes use of functions such as sl_send_reply or sl_gen_totag that trigger the vulnerable code.

Patches

This issue has been fixed by commit ab611f7.

References

Read more about this issue in the Audit Document section 3.10.

For more information

If you have any questions or comments about this advisory:

• Open an issue in the OpenSIPS GitHub
• Email us at [email protected]