CVE-2025-21629 (GCVE-0-2025-21629)
Vulnerability from cvelistv5
Published
2025-01-15 13:06
Modified
2026-08-05 11:53
Severity ?
8.2 (High) - CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:H
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.
References
Impacted products
Vendor Product Version
Linux Linux Version: a84978a9cda68f0afe3f01d476c68db21526baf1
Version: c69bc67c1cb211aa390bea6e512bb01b1241fefb
Version: 04c20a9356f283da623903e81e7c6d5df7e4dc3c
Version: 04c20a9356f283da623903e81e7c6d5df7e4dc3c
Version: bcefc3cd7f592a70fcbbbfd7ad1fbc69172ea78b
Version: 477b35d94a21530046fe91589960732fcf2b29ed
Version: a27a5c40ee4cbe00294e2c76160de5f2589061ba
Version: 9f605135a5c0fe614c2b15197b9ced1e217eca59
Version: 705350fbd6ed4b5d89ee045fa57a0594a72b17d7
Version: 6.1.116   ≤
Version: 6.6.60   ≤
Version: 4.19.323   ≤
Version: 5.4.285   ≤
Version: 5.10.229   ≤
Version: 5.15.171   ≤
Version: 6.11.7   ≤
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          "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nnet: reenable NETIF_F_IPV6_CSUM offload for BIG TCP packets\n\nThe blamed commit disabled hardware offoad of IPv6 packets with\nextension headers on devices that advertise NETIF_F_IPV6_CSUM,\nbased on the definition of that feature in skbuff.h:\n\n *   * - %NETIF_F_IPV6_CSUM\n *     - Driver (device) is only able to checksum plain\n *       TCP or UDP packets over IPv6. These are specifically\n *       unencapsulated packets of the form IPv6|TCP or\n *       IPv6|UDP where the Next Header field in the IPv6\n *       header is either TCP or UDP. IPv6 extension headers\n *       are not supported with this feature. This feature\n *       cannot be set in features for a device with\n *       NETIF_F_HW_CSUM also set. This feature is being\n *       DEPRECATED (see below).\n\nThe change causes skb_warn_bad_offload to fire for BIG TCP\npackets.\n\n[  496.310233] WARNING: CPU: 13 PID: 23472 at net/core/dev.c:3129 skb_warn_bad_offload+0xc4/0xe0\n\n[  496.310297]  ? skb_warn_bad_offload+0xc4/0xe0\n[  496.310300]  skb_checksum_help+0x129/0x1f0\n[  496.310303]  skb_csum_hwoffload_help+0x150/0x1b0\n[  496.310306]  validate_xmit_skb+0x159/0x270\n[  496.310309]  validate_xmit_skb_list+0x41/0x70\n[  496.310312]  sch_direct_xmit+0x5c/0x250\n[  496.310317]  __qdisc_run+0x388/0x620\n\nBIG TCP introduced an IPV6_TLV_JUMBO IPv6 extension header to\ncommunicate packet length, as this is an IPv6 jumbogram. But, the\nfeature is only enabled on devices that support BIG TCP TSO. The\nheader is only present for PF_PACKET taps like tcpdump, and not\ntransmitted by physical devices.\n\nFor this specific case of extension headers that are not\ntransmitted, return to the situation before the blamed commit\nand support hardware offload.\n\nipv6_has_hopopt_jumbo() tests not only whether this header is present,\nbut also that it is the only extension header before a terminal (L4)\nheader."
        }
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          "cvssV3_1": {
            "baseScore": 8.2,
            "baseSeverity": "HIGH",
            "vectorString": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:H",
            "version": "3.1"
          },
          "scenarios": [
            {
              "lang": "en",
              "value": "AV:N - The vulnerable code is in the core IPv6/TCP transmit path of net/core/dev.c and is driven by remote traffic \u2014 on a BIG-TCP router, `ipv6_gro_complete()` builds the offending jumbogram directly from received packets and forwards it out an affected NIC, and on a server a remote client requesting a large transfer makes the local stack emit one via `ip6_xmit()`. No local access is required.\nAC:L - On a BIG-TCP-enabled host with an affected NIC (bnxt/mlx4/ice or a bond/bridge over them) every IPv6 jumbogram deterministically takes the `sw_checksum` path and hits the WARN \u2014 there is no race, no timing window, and no memory-layout dependency; the attacker only has to move more than 64KB of TCP data.\nPR:N - No credentials are needed \u2014 forwarded transit traffic or an ordinary request to an unauthenticated network service is sufficient to make the victim emit a jumbogram. Locally, any unprivileged user with a TCP/IPv6 socket also reaches the same code with no capabilities.\nUI:N - Triggering requires only that the target transmit or forward IPv6 TCP data, which the attacker induces directly by sending or requesting traffic. No action by any local user or administrator is involved.\nS:U - The WARN, the packet drop and the log output all occur within the kernel\u0027s own security authority on the affected host; no VM, IOMMU, or sandbox boundary is crossed.\nC:L - The WARN path calls `skb_dump(KERN_WARNING, skb, false)`, which hex-dumps the packet\u0027s headers plus up to `MAX_HEADER + 128` bytes of in-flight payload, along with socket and device metadata, into the kernel log \u2014 a small, bounded disclosure of live network data readable by anyone with dmesg access. It is not an arbitrary read, so the leak is limited rather than high.\nI:N - There is no memory corruption and no out-of-bounds write; the affected packet is discarded by `kfree_skb()` in `validate_xmit_skb()` rather than transmitted with altered contents, so no data is modified.\nA:H - `skb_warn_bad_offload()` issues a `WARN(1, ...)`, which panics the machine outright on the many production and hardened deployments running with `panic_on_warn=1`; even without that, every BIG TCP packet is unconditionally dropped, breaking or severely degrading IPv6 TCP connectivity while flooding the log with splats and packet dumps."
            }
          ]
        }
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      "providerMetadata": {
        "dateUpdated": "2026-08-05T11:53:15.084Z",
        "orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
        "shortName": "Linux"
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      "references": [
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          "url": "https://git.kernel.org/stable/c/ac9cfef69565021c9e1022a493a9c40b03e2caf9"
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          "url": "https://git.kernel.org/stable/c/68e068cabd2c6c533ef934c2e5151609cf6ecc6d"
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      "title": "net: reenable NETIF_F_IPV6_CSUM offload for BIG TCP packets",
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    "assignerShortName": "Linux",
    "cveId": "CVE-2025-21629",
    "datePublished": "2025-01-15T13:06:00.128Z",
    "dateReserved": "2024-12-29T08:45:45.725Z",
    "dateUpdated": "2026-08-05T11:53:15.084Z",
    "state": "PUBLISHED"
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