CVE-2025-37959 bpf: Scrub packet on bpf_redirect_peer

Critical 9.4 Published 20 May 2025 Updated 15 Oct 2026

Attackers can leak network namespace data or cause traffic drops via improper packet scrubbing in bpf_redirect_peer, affecting Linux kernel users.

Exploited in the wild: Not known
Login needed: Not needed
Attackable: Over the internet
Victim action needed: Not needed
Fix: Available

What is CVE-2025-37959?

CVE-2025-37959 is a critical vulnerability in Debian Debian Linux, published on 20 May 2025. 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:

bpf: Scrub packet on bpf_redirect_peer

When bpf_redirect_peer is used to redirect packets to a device in another network namespace, the skb isn't scrubbed. That can lead skb information from one namespace to be "misused" in another namespace.

As one example, this is causing Cilium to drop traffic when using bpf_redirect_peer to redirect packets that just went through IPsec decryption to a container namespace. The following pwru trace shows (1) the packet path from the host's XFRM layer to the container's XFRM layer where it's dropped and (2) the number of active skb extensions at each function.

NETNS MARK IFACE TUPLE FUNC 4026533547 d00 eth0 10.244.3.124:35473->10.244.2.158:53 xfrm_rcv_cb .active_extensions = (__u8)2, 4026533547 d00 eth0 10.244.3.124:35473->10.244.2.158:53 xfrm4_rcv_cb .active_extensions = (__u8)2, 4026533547 d00 eth0 10.244.3.124:35473->10.244.2.158:53 gro_cells_receive .active_extensions = (__u8)2, [...] 4026533547 0 eth0 10.244.3.124:35473->10.244.2.158:53 skb_do_redirect .active_extensions = (__u8)2, 4026534999 0 eth0 10.244.3.124:35473->10.244.2.158:53 ip_rcv .active_extensions = (__u8)2, 4026534999 0 eth0 10.244.3.124:35473->10.244.2.158:53 ip_rcv_core .active_extensions = (__u8)2, [...] 4026534999 0 eth0 10.244.3.124:35473->10.244.2.158:53 udp_queue_rcv_one_skb .active_extensions = (__u8)2, 4026534999 0 eth0 10.244.3.124:35473->10.244.2.158:53 __xfrm_policy_check .active_extensions = (__u8)2, 4026534999 0 eth0 10.244.3.124:35473->10.244.2.158:53 __xfrm_decode_session .active_extensions = (__u8)2, 4026534999 0 eth0 10.244.3.124:35473->10.244.2.158:53 security_xfrm_decode_session .active_extensions = (__u8)2, 4026534999 0 eth0 10.244.3.124:35473->10.244.2.158:53 kfree_skb_reason(SKB_DROP_REASON_XFRM_POLICY) .active_extensions = (__u8)2,

In this case, there are no XFRM policies in the container's network namespace so the drop is unexpected. When we decrypt the IPsec packet, the XFRM state used for decryption is set in the skb extensions. This information is preserved across the netns switch. When we reach the XFRM policy check in the container's netns, __xfrm_policy_check drops the packet with LINUX_MIB_XFRMINNOPOLS because a (container-side) XFRM policy can't be found that matches the (host-side) XFRM state used for decryption.

This patch fixes this by scrubbing the packet when using bpf_redirect_peer, as is done on typical netns switches via veth devices except skb->mark and skb->tstamp are not zeroed.

Which versions are affected by CVE-2025-37959?

It affects 2 products.

Products include Debian Debian Linux, Linux kernel.

How do I fix CVE-2025-37959?

Apply the vendor's patch.

Is CVE-2025-37959 being exploited?

There is no known exploitation of CVE-2025-37959 in the wild and no public exploit code.

All Debian Debian Linux vulnerabilities

Sources

Also known as AZL-72572, BELL-CVE-2025-37959, DEBIAN-CVE-2025-37959, GHSA-g5rc-wjvg-94w5, ROOT-OS-DEBIAN-11-CVE-2025-37959, ROOT-OS-DEBIAN-12-CVE-2025-37959 and 3 more.