CVE-2025-21629: Linux kernel · net: reenable NETIF_F_IPV6_CSUM offload for BIG TCP packets
Affects Linux kernelSource GCVE Database
Not known to be exploited · CVSS 8.2 High · fixed in 6.11.0-21.21~24.04.1 : patch Linux kernel soon.
Data as of 26 Oct 2026, 10:12 UTC
- EPSS
- 0.4% chance of exploitation in 30 days – higher than 36% of CVEsExploit Prediction Scoring System: the likelihood attackers will use this flaw soon.
- Patch
- Available – fixed in 6.11.0-21.21~24.04.1, 6.11.0-1017.17
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:HExploitation evidence
Disclosed: evidence found.
CVE published 15 Jan 2025
Detectable: no evidence on record.
No public nuclei template indexed
Weaponised: no evidence on record.
No public exploit code indexed in Metasploit or Exploit-DB
Exploited in the wildExploited: no evidence on record.
Not in CISA KEV and no source reports exploitation
Observed by OffSeq MirageSeen by Mirage: no evidence on record.
No attack traffic recorded by OffSeq Mirage sensors
A missing step is not evidence of safety. Sources: cve.org (opens in a new tab), the Metasploit, Exploit-DB and nuclei-templates index as of 26 Oct 2026.
What to do
Upgrade the Ubuntu to 6.11.0-21.21~24.04.1 (linux-hwe-6.11 package) or 6.11.0-1017.17 (linux-oem-6.11 package).
Affected software
| Product | Affected | Fixed in |
|---|---|---|
Ubuntu 24.04 LTSlinux-hwe-6.11pkg:deb/ubuntu/linux-hwe-6.11@6.11.0-21.21~24.04.1?arch=source&distro=nobleOther threats | Affected
| Fixed in
|
Ubuntu 24.04 LTSlinux-oem-6.11pkg:deb/ubuntu/linux-oem-6.11@6.11.0-1017.17?arch=source&distro=nobleOther threats | Affected
| Fixed in
|
Ubuntu 24.04 LTSlinux-raspi-realtimepkg:deb/ubuntu/linux-raspi-realtime@6.8.0-2019.20?arch=source&distro=nobleOther threats | Affected
| Fixed in– |
Ubuntu Nvidia-BlueField 24.04 LTSlinux-bluefieldpkg:deb/ubuntu/linux-bluefield@6.8.0-1026.30?arch=source&distro=bluefield/nobleOther threats | Affected
| Fixed in– |
Ubuntu 22.04 LTSlinuxpkg:deb/ubuntu/linux@5.15.0-186.196?arch=source&distro=jammyOther threats | Affected
| Fixed in– |
Ubuntu 22.04 LTSlinux-allwinner-5.19pkg:deb/ubuntu/linux-allwinner-5.19@5.19.0-1015.15~22.04.1?arch=source&distro=jammyOther threats | Affected
| Fixed in– |
Check your own hosts for these packages with threat-finder (opens in a new tab), our free open-source scanner.
Description
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.
References
- ubuntu.com/security/CVE-2025-21629 (opens in a new tab)
- cve.org/CVERecord?id=CVE-2025-21629 (opens in a new tab)
- git.kernel.org/linus/68e068cabd2c6c533ef934c2e5151609cf6ecc6d (opens in a new tab)
- git.kernel.org/stable/c/68e068cabd2c6c533ef934c2e5151609cf6ecc6d (opens in a new tab)
- git.kernel.org/stable/c/95ccf006bbc8b59044313b8c309dcf29c546abd4 (opens in a new tab)
- git.kernel.org/stable/c/ac9cfef69565021c9e1022a493a9c40b03e2caf9 (opens in a new tab)
- git.kernel.org/stable/c/d3b7a9c7597b779039a51d7b34116fbe424bf2b7 (opens in a new tab)
- ubuntu.com/security/notices/USN-7379-1 (opens in a new tab)
- ubuntu.com/security/notices/USN-7380-1 (opens in a new tab)
- ubuntu.com/security/notices/USN-7381-1 (opens in a new tab)
- ubuntu.com/security/notices/USN-7382-1 (opens in a new tab)
- ubuntu.com/security/notices/USN-7379-2 (opens in a new tab)