CVE-2025-68363
Low risk· EPSS 7%Exploitation Probability (EPSS)
Low risk7th percentile - higher than 7% of all known CVEs
Summary
A vulnerability was found in the Linux kernel's BPF helper `bpf_skb_check_mtu`. When the `BPF_MTU_CHK_SEGS` flag is used, the helper requires the `transport_header` field in the `skb` structure to be set, which is not always the case. Missing this setting triggers a WARN_ON_ONCE warning and may cause incorrect behavior, especially during tests with `bpf_prog_test_run`.
Risk Assessment
The risk involves a possible kernel warning (WARN_ON_ONCE) and potential malfunction of the MTU checking function, which could affect system stability or allow packets of incorrect size to pass.
Recommendation
Apply the Linux kernel patch containing the commit that fixes this issue. It is recommended to update to the latest stable kernel version or backport the appropriate fix.
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Original NVD description (English source)
In the Linux kernel, the following vulnerability has been resolved: bpf: Check skb->transport_header is set in bpf_skb_check_mtu The bpf_skb_check_mtu helper needs to use skb->transport_header when the BPF_MTU_CHK_SEGS flag is used: bpf_skb_check_mtu(skb, ifindex, &mtu_len, 0, BPF_MTU_CHK_SEGS) The transport_header is not always set. There is a WARN_ON_ONCE report when CONFIG_DEBUG_NET is enabled + skb->gso_size is set + bpf_prog_test_run is used: WARNING: CPU: 1 PID: 2216 at ./include/linux/skbuff.h:3071 skb_gso_validate_network_len bpf_skb_check_mtu bpf_prog_3920e25740a41171_tc_chk_segs_flag # A test in the next patch bpf_test_run bpf_prog_test_run_skb For a normal ingress skb (not test_run), skb_reset_transport_header is performed but there is plan to avoid setting it as described in commit 2170a1f09148 ("net: no longer reset transport_header in __netif_receive_skb_core()"). This patch fixes the bpf helper by checking skb_transport_header_was_set(). The check is done just before skb->transport_header is used, to avoid breaking the existing bpf prog. The WARN_ON_ONCE is limited to bpf_prog_test_run, so targeting bpf-next.

