CVE-2026-90054 (GCVE-0-2026-90054)
Vulnerability from cvelistv5
Published
2026-09-17 16:05
Modified
2026-10-19 08:57
Severity ?
Summary
In the Linux kernel, the following vulnerability has been resolved: tcp: fix corruption of urgent data on multi-segment retransmit On the normal xmit path, while in urgent mode we refuse to build a multi-segment TSO packet, so every segment gets its own urg_ptr: /* tcp_write_xmit() */ limit = mss_now; if (tso_segs > 1 && !tcp_urg_mode(tp)) limit = tcp_mss_split_point(...); The retransmit path has no such guard. __tcp_retransmit_skb() builds a segs > 1 skb and hands it to the GSO layer, which only advances th->seq per segment and copies urg_ptr verbatim: /* __tcp_retransmit_skb() */ len = cur_mss * segs; /* segs > 1, no urg_mode check */ ... /* tcp_gso_segment(): bumps seq only, urg_ptr is copied */ urg_ptr is an offset from the segment's own seq, so a copied value points at a different place on each segment. The receiver rebuilds the absolute urgent seq as seg.seq + urg_ptr, so it walks a moving urgent point instead of the one OOB byte: seg1 seq 1 urg_ptr 5001 -> urgent @ 5001 (ok) seg2 seq 1001 urg_ptr 5001 -> urgent @ 6001 (wrong, +MSS) seg3 seq 2001 urg_ptr 5001 -> urgent @ 7001 (wrong, +2*MSS) The real OOB byte is never pointed at, so the receiver stops splicing it out and delivers it as normal in-band data, corrupting the stream. Guard the retransmit length like the xmit path: keep segs = 1 while in urgent mode.
References
Impacted products
Vendor Product Version
Linux Linux Version: 10d3be569243def8d92ac3722395ef5a59c504e6
Version: 10d3be569243def8d92ac3722395ef5a59c504e6
Version: 10d3be569243def8d92ac3722395ef5a59c504e6
Version: 10d3be569243def8d92ac3722395ef5a59c504e6
Version: 10d3be569243def8d92ac3722395ef5a59c504e6
Version: 10d3be569243def8d92ac3722395ef5a59c504e6
Version: 10d3be569243def8d92ac3722395ef5a59c504e6
Version: 10d3be569243def8d92ac3722395ef5a59c504e6
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{
  "containers": {
    "cna": {
      "affected": [
        {
          "defaultStatus": "unaffected",
          "product": "Linux",
          "programFiles": [
            "net/ipv4/tcp_output.c"
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          "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
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              "version": "6.1.188",
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              "version": "7.2.6",
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              "status": "unaffected",
              "version": "7.3",
              "versionType": "original_commit_for_fix"
            }
          ]
        }
      ],
      "cpeApplicability": [
        {
          "nodes": [
            {
              "cpeMatch": [
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              ],
              "negate": false,
              "operator": "OR"
            }
          ]
        }
      ],
      "descriptions": [
        {
          "lang": "en",
          "value": "In the Linux kernel, the following vulnerability has been resolved:\n\ntcp: fix corruption of urgent data on multi-segment retransmit\n\nOn the normal xmit path, while in urgent mode we refuse to build a\nmulti-segment TSO packet, so every segment gets its own urg_ptr:\n\n\t/* tcp_write_xmit() */\n\tlimit = mss_now;\n\tif (tso_segs \u003e 1 \u0026\u0026 !tcp_urg_mode(tp))\n\t\tlimit = tcp_mss_split_point(...);\n\nThe retransmit path has no such guard. __tcp_retransmit_skb() builds a\nsegs \u003e 1 skb and hands it to the GSO layer, which only advances th-\u003eseq\nper segment and copies urg_ptr verbatim:\n\n\t/* __tcp_retransmit_skb() */\n\tlen = cur_mss * segs;\t\t/* segs \u003e 1, no urg_mode check */\n\t...\n\t/* tcp_gso_segment(): bumps seq only, urg_ptr is copied */\n\nurg_ptr is an offset from the segment\u0027s own seq, so a copied value points\nat a different place on each segment. The receiver rebuilds the absolute\nurgent seq as seg.seq + urg_ptr, so it walks a moving urgent point instead\nof the one OOB byte:\n\n\tseg1  seq 1     urg_ptr 5001 -\u003e urgent @ 5001   (ok)\n\tseg2  seq 1001  urg_ptr 5001 -\u003e urgent @ 6001   (wrong, +MSS)\n\tseg3  seq 2001  urg_ptr 5001 -\u003e urgent @ 7001   (wrong, +2*MSS)\n\nThe real OOB byte is never pointed at, so the receiver stops splicing it\nout and delivers it as normal in-band data, corrupting the stream.\n\nGuard the retransmit length like the xmit path: keep segs = 1 while in\nurgent mode."
        }
      ],
      "providerMetadata": {
        "dateUpdated": "2026-10-19T08:57:11.615Z",
        "orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
        "shortName": "Linux"
      },
      "references": [
        {
          "url": "https://git.kernel.org/stable/c/8eb51013b6308870479a64b4a2a018697b997849"
        },
        {
          "url": "https://git.kernel.org/stable/c/711bfd762bec05fb19bc3b17cbb157c39f4e66da"
        },
        {
          "url": "https://git.kernel.org/stable/c/3d4e005c198dc410ad568f832bffa7569c059ff8"
        },
        {
          "url": "https://git.kernel.org/stable/c/4fd2ee4ac154c204d95d8db72221446dac5af9b8"
        },
        {
          "url": "https://git.kernel.org/stable/c/ebe55406404f3cb28e36d2b668e2c6c05026ec29"
        },
        {
          "url": "https://git.kernel.org/stable/c/b8f08a94b2a4addc39249dcf9c792e786108621b"
        },
        {
          "url": "https://git.kernel.org/stable/c/47eb90299e6882d6445672530dd7c51ac33ebdbd"
        },
        {
          "url": "https://git.kernel.org/stable/c/ce2b807f42ed5e55567b8864ab72963f90779270"
        }
      ],
      "title": "tcp: fix corruption of urgent data on multi-segment retransmit",
      "x_generator": {
        "engine": "bippy-1.2.0"
      }
    }
  },
  "cveMetadata": {
    "assignerOrgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
    "assignerShortName": "Linux",
    "cveId": "CVE-2026-90054",
    "datePublished": "2026-09-17T16:05:39.632Z",
    "dateReserved": "2026-09-11T19:38:34.783Z",
    "dateUpdated": "2026-10-19T08:57:11.615Z",
    "state": "PUBLISHED"
  },
  "dataType": "CVE_RECORD",
  "dataVersion": "5.2"
}


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