CVE-2026-31427

In the Linux kernel, the following vulnerability has been resolved:

netfilter: nf_conntrack_sip: fix use of uninitialized rtp_addr in process_sdp

process_sdp() declares union nf_inet_addr rtp_addr on the stack and

passes it to the nf_nat_sip sdp_session hook after walking the SDP

media descriptions. However rtp_addr is only initialized inside the

media loop when a recognized media type with a non-zero port is found.

If the SDP body contains no m= lines, only inactive media sections

(m=audio 0 ...) or only unrecognized media types, rtp_addr is never

assigned. Despite that, the function still calls hooks->sdp_session()

with &rtp_addr, causing nf_nat_sdp_session() to format the stale stack

value as an IP address and rewrite the SDP session owner and connection

lines with it.

With CONFIG_INIT_STACK_ALL_ZERO (default on most distributions) this

results in the session-level o= and c= addresses being rewritten to

0.0.0.0 for inactive SDP sessions. Without stack auto-init the

rewritten address is whatever happened to be on the stack.

Fix this by pre-initializing rtp_addr from the session-level connection

address (caddr) when available, and tracking via a have_rtp_addr flag

whether any valid address was established. Skip the sdp_session hook

entirely when no valid address exists.