CVE-2026-52986 netfilter: nf_conntrack_sip: don't use simple_strtoul
A null pointer dereference in the Linux kernel SIP conntrack helper allows remote attackers to cause a denial of service via malformed packets.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-52986?
CVE-2026-52986 is a critical vulnerability in Linux kernel, published on 24 Jun 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Official description
In the Linux kernel, the following vulnerability has been resolved:
netfilter: nf_conntrack_sip: don't use simple_strtoul
Replace unsafe port parsing in epaddr_len(), ct_sip_parse_header_uri(), and ct_sip_parse_request() with a new sip_parse_port() helper that validates each digit against the buffer limit, eliminating the use of simple_strtoul() which assumes NUL-terminated strings.
The previous code dereferenced pointers without bounds checks after sip_parse_addr() and relied on simple_strtoul() on non-NUL-terminated skb data. A port that reaches the buffer limit without a trailing character is also rejected as malformed.
Also get rid of all simple_strtoul() usage in conntrack, prefer a stricter version instead. There are intentional changes:
- Bail out if number is > UINT_MAX and indicate a failure, same for too long sequences. While we do accept 05535 as port 5535, we will not accept e.g. 'sip:10.0.0.1:005060'. While its syntactically valid under RFC 3261, we should restrict this to not waste cycles when presented with malformed packets with 64k '0' characters.
- Force base 10 in ct_sip_parse_numerical_param(). This is used to fetch 'expire=' and 'rports='; both are expected to use base-10.
- In nf_nat_sip.c, only accept the parsed value if its within the 1k-64k range.
- epaddr_len now returns 0 if the port is invalid, as it already does for invalid ip addresses. This is intentional. nf_conntrack_sip performs lots of guesswork to find the right parts of the message to parse. Being stricter could break existing setups. Connection tracking helpers are designed to allow traffic to pass, not to block it.
Based on an earlier patch from Jenny Guanni Qu <[email protected]>.
Which versions are affected by CVE-2026-52986?
It affects 1 product.
Products include Linux kernel.
How do I fix CVE-2026-52986?
Apply the vendor's patch.
Is CVE-2026-52986 being exploited?
There is no known exploitation of CVE-2026-52986 in the wild and no public exploit code.
Other vulnerabilities in Linux kernel
Sources
Also known as BELL-CVE-2026-52986, DEBIAN-CVE-2026-52986, GHSA-p6jx-f9x6-6955, ROOT-OS-DEBIAN-11-CVE-2026-52986, ROOT-OS-DEBIAN-12-CVE-2026-52986, ROOT-OS-UBUNTU-2204-CVE-2026-52986 and 2 more.