Is CVE-2025-21629 being actively exploited?

It is not currently in CISA's KEV catalog. Its EPSS exploitation probability is 0%.

What products does CVE-2025-21629 affect?

Tracked products affected include Linux Kernel. Check the version you run to see whether it is affected.

How do I fix CVE-2025-21629?

Apply the vendor fix promptly. An official patch or advisory is available. Upgrade affected products to a fixed version.

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CVE-2025-21629

Q: What is CVE-2025-21629?

CVE-2025-21629 is a high-severity software vulnerability with a CVSS score of 8.2. In the Linux kernel, the following vulnerability has been resolved: net: reenable NETIF_F_IPV6_CSUM offload for BIG TCP packets The blamed commit disabled hardware offoad of IPv6 packets with extension headers on devices that advertise NE

HIGH severity · CVSS 8.2

8.2CVSS HIGH

Summary

In the Linux kernel, the following vulnerability has been resolved: net: reenable NETIF_F_IPV6_CSUM offload for BIG TCP packets The blamed commit disabled hardware offoad of IPv6 packets with extension headers on devices that advertise NETIF_F_IPV6_CSUM, based on the definition of that feature in skbuff.h: * * - %NETIF_F_IPV6_CSUM * - Driver (device) is only able to checksum plain * TCP or UDP packets over IPv6. These are specifically * unencapsulated packets of the form IPv6|TCP or * IPv6|UDP where the Next Header field in the IPv6 * header is either TCP or UDP. IPv6 extension headers * are not supported with this feature. This feature * cannot be set in features for a device with * NETIF_F_HW_CSUM also set. This feature is being * DEPRECATED (see below). The change causes skb_warn_bad_offload to fire for BIG TCP packets. [ 496.310233] WARNING: CPU: 13 PID: 23472 at net/core/dev.c:3129 skb_warn_bad_offload+0xc4/0xe0 [ 496.310297] ? skb_warn_bad_offload+0xc4/0xe0 [ 496.310300] skb_checksum_help+0x129/0x1f0 [ 496.310303] skb_csum_hwoffload_help+0x150/0x1b0 [ 496.310306] validate_xmit_skb+0x159/0x270 [ 496.310309] validate_xmit_skb_list+0x41/0x70 [ 496.310312] sch_direct_xmit+0x5c/0x250 [ 496.310317] __qdisc_run+0x388/0x620 BIG TCP introduced an IPV6_TLV_JUMBO IPv6 extension header to communicate packet length, as this is an IPv6 jumbogram. But, the feature is only enabled on devices that support BIG TCP TSO. The header is only present for PF_PACKET taps like tcpdump, and not transmitted by physical devices. For this specific case of extension headers that are not transmitted, return to the situation before the blamed commit and support hardware offload. ipv6_has_hopopt_jumbo() tests not only whether this header is present, but also that it is the only extension header before a terminal (L4) header.

Impact & exploitability

Attack vectorNetwork

Attack complexityLow

Privileges requiredNone

User interactionNone

Confidentiality impactLow

Integrity impactNone

Availability impactHigh

Exploit probability (EPSS)0%

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:H

Affected products we track (1)

Linux Kernel

Recommendation

Apply the vendor fix promptly. Open any affected product above for its exact safe version.

Official patch: https://git.kernel.org/stable/c/68e068cabd2c6c533ef934c2e5151609cf6ecc6d ↗

CVE-2025-21629

Summary

Impact & exploitability

Affected products we track (1)

Recommendation

Additional information