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CVE-2026-90054 Affecting linux-6.12 package, versions <6.12.111-1~deb12u1

Severity

 Recommended
low

Based on default assessment until relevant scores are available.

Threat Intelligence

EPSS
0.22% (12th percentile)

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  • Snyk IDSNYK-DEBIAN12-LINUX612-20507143
  • published5 Oct 2026
  • disclosed17 Sept 2026
Report a new vulnerability Found a mistake?

Introduced: 17 Sep 2026

NewCVE-2026-90054  (opens in a new tab)

How to fix?

Upgrade Debian:12 linux-6.12 to version 6.12.111-1~deb12u1 or higher.

NVD Description

Note: Versions mentioned in the description apply only to the upstream linux-6.12 package and not the linux-6.12 package as distributed by Debian. See How to fix? for Debian:12 relevant fixed versions and status.

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 &gt; 1 &amp;&amp; !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 &gt; 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 -&gt; urgent @ 5001   (ok)
seg2  seq 1001  urg_ptr 5001 -&gt; urgent @ 6001   (wrong, +MSS)
seg3  seq 2001  urg_ptr 5001 -&gt; 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.