CVE-2026-23457 — netfilter: nf_conntrack_sip: fix Content-Length u32 truncation in sip_help_tcp()

Affected: Linux, Siemens SIMATIC S7-1500 CPU 1518-4 PN/DP MFP, Siemens SIMATIC S7-1500 CPU 1518F-4 PN/DP MFP, Siemens SIPLUS S7-1500 CPU 1518-4 PN/DP MFP

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

netfilter: nf_conntrack_sip: fix Content-Length u32 truncation in sip_help_tcp()

sip_help_tcp() parses the SIP Content-Length header with simple_strtoul(), which returns unsigned long, but stores the result in unsigned int clen. On 64-bit systems, values exceeding UINT_MAX are silently truncated before computing the SIP message boundary.

For example, Content-Length 4294967328 (2^32 + 32) is truncated to 32, causing the parser to miscalculate where the current message ends. The loop then treats trailing data in the TCP segment as a second SIP message and processes it through the SDP parser.

Fix this by changing clen to unsigned long to match the return type of simple_strtoul(), and reject Content-Length values that exceed the remaining TCP payload length.

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CVE-2026-23457 — netfilter: nf_conntrack_sip: fix Content-Length u32 truncation in sip_help_tcp()