{"id":"CVE-2026-90054","published":"2026-09-17T17:16:53.873","lastModified":"2026-09-17T17:16:53.873","description":"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 > 1 && !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 > 1 skb and hands it to the GSO layer, which only advances th->seq\nper segment and copies urg_ptr verbatim:\n\n\t/* __tcp_retransmit_skb() */\n\tlen = cur_mss * segs;\t\t/* segs > 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's 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 -> urgent @ 5001   (ok)\n\tseg2  seq 1001  urg_ptr 5001 -> urgent @ 6001   (wrong, +MSS)\n\tseg3  seq 2001  urg_ptr 5001 -> 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.","cvssScore":null,"cvssSeverity":null,"cvssVector":null,"cwes":[],"vendors":[],"products":[],"references":[{"url":"https://git.kernel.org/stable/c/3d4e005c198dc410ad568f832bffa7569c059ff8","tags":[]},{"url":"https://git.kernel.org/stable/c/47eb90299e6882d6445672530dd7c51ac33ebdbd","tags":[]},{"url":"https://git.kernel.org/stable/c/4fd2ee4ac154c204d95d8db72221446dac5af9b8","tags":[]},{"url":"https://git.kernel.org/stable/c/711bfd762bec05fb19bc3b17cbb157c39f4e66da","tags":[]},{"url":"https://git.kernel.org/stable/c/8eb51013b6308870479a64b4a2a018697b997849","tags":[]},{"url":"https://git.kernel.org/stable/c/b8f08a94b2a4addc39249dcf9c792e786108621b","tags":[]},{"url":"https://git.kernel.org/stable/c/ce2b807f42ed5e55567b8864ab72963f90779270","tags":[]},{"url":"https://git.kernel.org/stable/c/ebe55406404f3cb28e36d2b668e2c6c05026ec29","tags":[]}],"exploitRefs":[],"hasPoc":false,"ai":null}