In the Linux kernel, the following vulnerability has been resolved:
netfilter: nf_nat_sip: reload possible stale data pointer
quoting sashiko:
<hr />
[..] noticed a potential memory bug and header corruption involving the
SIP NAT helper.
In net/netfilter/nf_nat_sip.c:nf_nat_sip():
if (skb_ensure_writable(skb, skb->len)) {
nf_ct_helper_log(skb, ct, "cannot mangle packet");
return NF_DROP;
}
uh = (void *)skb->data + protoff;
uh->dest = ct_sip_info->forced_dport;
if (!nf_nat_mangle_udp_packet(skb, ct, ctinfo, protoff,
0, 0, NULL, 0)) {
If a cloned or fragmented SKB is reallocated by skb_ensure_writable(), the
old data buffer is freed. However, nf_nat_sip() fails to update *dptr to
point to the new buffer.
It also appears to use nf_nat_mangle_udp_packet() on what could be a TCP
packet, which would overwrite the sequence number with a checksum update.
<hr />
nf_conntrack_sip linerizes skbs, hence no fragmented skb can be seen.
But clones are possible, so rebuild dptr.
Disable nf_nat_mangle_udp_packet() branch for TCP streams.
It doesn't look like this can ever happen, else we should have received
bug reports about this, so just check the conntrack is UDP and drop
otherwise.
The calling conntrack_sip set ->forced_dport for SIP_HDR_VIA_UDP messages,
so I don't think this is ever expected to be true for a TCP stream.
CVSS Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
CVSS Score: 9.8
AV:N - The bug is hit in nf_nat_sip() from sip_help_udp/tcp() during nf_confirm() on POST_ROUTING/LOCAL_IN while processing attacker-supplied SIP/UDP or SIP/TCP packets traversing a netfilter NAT gateway, so exploitation is via remote network traffic rather than local syscalls or physical access.
AC:L - Once nf_conntrack_sip and nf_nat_sip are active on a NATed SIP flow, a remote peer can set forced_dport with a crafted Via header and drive the reply-path skb_ensure_writable() reallocation on cloned skbs without races or rare layout luck.
PR:N - Exploitation needs no privileges on the victim kernel; a remote SIP endpoint only has to send malicious SIP through an already-configured SIP conntrack/NAT helper, with no authentication or local access to the firewall or router.
UI:N - No victim user action is required beyond normal automated packet forwarding; the SIP helper parses and NAT-rewrites attacker-supplied SIP data in softirq during connection-tracking confirmation without opening files, clicking links, or mounting filesystems.
S:U - Impact stays within kernel netfilter/conntrack memory on the same security authority (for example a NAT firewall, SBC, or VoIP gateway). This is standard kernel memory corruption, not a VM escape, sandbox breakout, or cross-tenant boundary violation.
C:H - skb_ensure_writable() can free the old linear buffer while *dptr still points into it; sip_help_tcp() then continues parsing with that stale pointer, giving a use-after-free read of freed skb data and enabling disclosure of adjacent kernel heap contents.
I:H - The stale dptr UAF and, on TCP flows, mistaken nf_nat_mangle_udp_packet() header rewriting corrupt kernel packet-buffer memory; such heap corruption is exploitable with grooming for arbitrary writes, control-flow hijacking, and kernel code execution.
A:H - Use-after-free and mis-mangled L4 headers during softirq SIP NAT processing can trigger kernel oops/panic or reliably drop or corrupt in-flight VoIP signaling, causing high availability impact on internet-facing NAT/SBC systems handling SIP.
| Attack Vector |
Network |
Scope |
Unchanged |
| Attack Complexity |
Low |
Confidentiality Impact |
High |
| Privileges Required |
None |
Integrity Impact |
High |
| User Interaction |
None |
Availability Impact |
High |
AV:N - The bug is hit in nf_nat_sip() from sip_help_udp/tcp() during nf_confirm() on POST_ROUTING/LOCAL_IN while processing attacker-supplied SIP/UDP or SIP/TCP packets traversing a netfilter NAT gateway, so exploitation is via remote network traffic rather than local syscalls or physical access.
AC:L - Once nf_conntrack_sip and nf_nat_sip are active on a NATed SIP flow, a remote peer can set forced_dport with a crafted Via header and drive the reply-path skb_ensure_writable() reallocation on cloned skbs without races or rare layout luck.
PR:N - Exploitation needs no privileges on the victim kernel; a remote SIP endpoint only has to send malicious SIP through an already-configured SIP conntrack/NAT helper, with no authentication or local access to the firewall or router.
UI:N - No victim user action is required beyond normal automated packet forwarding; the SIP helper parses and NAT-rewrites attacker-supplied SIP data in softirq during connection-tracking confirmation without opening files, clicking links, or mounting filesystems.
S:U - Impact stays within kernel netfilter/conntrack memory on the same security authority (for example a NAT firewall, SBC, or VoIP gateway). This is standard kernel memory corruption, not a VM escape, sandbox breakout, or cross-tenant boundary violation.
C:H - skb_ensure_writable() can free the old linear buffer while *dptr still points into it; sip_help_tcp() then continues parsing with that stale pointer, giving a use-after-free read of freed skb data and enabling disclosure of adjacent kernel heap contents.
I:H - The stale dptr UAF and, on TCP flows, mistaken nf_nat_mangle_udp_packet() header rewriting corrupt kernel packet-buffer memory; such heap corruption is exploitable with grooming for arbitrary writes, control-flow hijacking, and kernel code execution.
A:H - Use-after-free and mis-mangled L4 headers during softirq SIP NAT processing can trigger kernel oops/panic or reliably drop or corrupt in-flight VoIP signaling, causing high availability impact on internet-facing NAT/SBC systems handling SIP.
CVSS 3.1