From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id A08C24F0535 for ; Fri, 4 Sep 2026 15:57:04 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1788537426; cv=none; b=S9FXPh/g07Y3QAXTnV37LOEctt+vrMzWCjk800iv6OssbdGkxFvDiXNjOI3/3x3bolu8o7YmAUslKKbgTab6m3rCTxFlrS79hZnmva463tEyqUPJYiEsa+tcfBsz8Cpjh3w1AJp3WTZVL+WCkn+noE3u9avQQi0FhoeW2IEUE8I= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1788537426; c=relaxed/simple; bh=A89Led7HQBcZXC9XkM2jubivgIKmjebj3L0J1or0FUc=; h=From:To:Cc:Subject:Date:Message-ID:MIME-Version; b=uqHauxWogkznag/ygtpTuVmhAoT01aEZuqylDpWbwKeTsPYwnifltXqWMfd5mXr2/CWsATLLSQzE9XSQgxafjNMpFPM2+5NTPIOIUOSC0FTgFo7vp5+LqdwliP+S5454rjxU7nyu/ylokQBa571lpYvj+Yr1hj1RHGczQ1i6ZmI= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=Z6LInrj0; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b="Z6LInrj0" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 426B51F00A3D; Fri, 4 Sep 2026 15:57:02 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linuxfoundation.org; s=korg; t=1788537424; bh=/KoPksYw6kKdu2qQ0vEGSfAnu8Yrdc2U69z8Zw8n3r4=; h=From:To:Cc:Subject:Date:Reply-To; b=Z6LInrj0JTwsPX0GIbXu9a8n0z92o4D2ApXwrUdudF82mUkmk7W3a41hHJZ2XUwB8 VfGnYhs3bCt+uXrYh7PlvxRWdA12MgH2YS/fNyLm+j9ZEWJX3b1hgMuApk8EfiAj7r AEVeaJDqw4mICY5aPaGG/nAFnk9QVwpz3YHt5O8o= From: Greg Kroah-Hartman To: linux-cve-announce@vger.kernel.org Cc: Greg Kroah-Hartman Subject: CVE-2026-80840: ipv6: seg6: clear IPv4 control block on IPIP decapsulation Date: Fri, 4 Sep 2026 17:53:07 +0200 Message-ID: <2026090457-CVE-2026-80840-54d7@gregkh> X-Mailer: git-send-email 2.55.0 Reply-To: , Precedence: bulk X-Mailing-List: linux-cve-announce@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-Developer-Signature: v=1; a=openpgp-sha256; l=6027; i=gregkh@linuxfoundation.org; h=from:subject:message-id; bh=oPJRwdIPJn2yDWKBd/2js1rJXyrBCBSH6ngZiMf7qpI=; b=owGbwMvMwCRo6H6F97bub03G02pJDFmzXkYd+5X3Z7Zo9839kXkb7Zt+eT53bZL5OFHt/6+jG /KiexKSO2JZGASZGGTFFFm+bOM5ur/ikKKXoe1pmDmsTCBDGLg4BWAial8ZZrMUti8N8/7zyz97 4aZNGtXqhz66+DMsWLJlfcAH21mGRtWBZv9jwloN46dkAgA= X-Developer-Key: i=gregkh@linuxfoundation.org; a=openpgp; fpr=F4B60CC5BF78C2214A313DCB3147D40DDB2DFB29 Content-Transfer-Encoding: 8bit From: Greg Kroah-Hartman Description =========== In the Linux kernel, the following vulnerability has been resolved: ipv6: seg6: clear IPv4 control block on IPIP decapsulation End.DX4 and End.DT4 decapsulate an IPv4 packet through decap_and_validate() and send it directly to IPv4 routing. The inner packet therefore bypasses ip_rcv_core(), which normally clears IPCB before IPv4 interprets skb->cb. The skb instead retains IP6CB data from the outer packet. IP6CB and IPCB use the same skb->cb storage, so IP6CB(skb)->lastopt overlaps IPCB(skb)->opt.optlen and srr, while IP6CB(skb)->nhoff overlaps rr and ts. The sender can make the stale optlen byte nonzero with a valid outer extension-header chain. The reproducers put an eight-byte Destination Options header immediately after the 40-byte IPv6 header and before the Segment Routing Header. ipv6_destopt_rcv() records the sender-controlled Destination Options offset in both lastopt and nhoff, setting them to 40. On the reproduced little-endian x86-64 kernel, IPv4 therefore sees optlen = 40 and rr = 40. Both tcp_v4_save_options() and __ip_options_echo() skip option copying when optlen is zero. Here optlen is 40, so the TCP SYN path allocates room for 40 bytes of option data and calls __ip_options_echo(). The stale rr value makes that function read inner packet byte 41 as the Record Route option length. The reproducers set that sender-controlled byte to 255, so __ip_options_echo() copies 255 bytes into the 40-byte option-data area. Separate End.DX4 and End.DT4 reproducers on the unpatched v7.2-rc5 kernel both produced: BUG: KASAN: slab-out-of-bounds in __ip_options_echo() Write of size 255 The relevant End.DX4 call path is: __ip_options_echo tcp_v4_route_req tcp_conn_request tcp_v4_conn_request tcp_rcv_state_process tcp_v4_do_rcv tcp_v4_rcv ip_protocol_deliver_rcu ip_local_deliver_finish ip_local_deliver input_action_end_dx4_finish input_action_end_dx4 The relevant End.DT4 call path is: __ip_options_echo tcp_v4_route_req tcp_conn_request tcp_v4_conn_request tcp_rcv_state_process tcp_v4_do_rcv tcp_v4_rcv ip_protocol_deliver_rcu ip_local_deliver_finish ip_local_deliver input_action_end_dt4 tcp_v4_save_options() is inlined into the tcp_v4_route_req() path, so it does not appear as a separate frame. When decap_and_validate() handles IPPROTO_IPIP, save the ingress interface from IP6CB, clear IPCB, and restore the saved value. Doing this in the common decapsulation path covers End.DX4, End.DT4, and End.DT46's IPv4 arm. Use IP6CB(skb)->iif rather than skb->skb_iif. These actions run after l3mdev processing, which can replace skb_iif with the L3 master; IP6CB iif still records the receiving interface set at IPv6 ingress. The Linux kernel CVE team has assigned CVE-2026-80840 to this issue. Affected and fixed versions =========================== Issue introduced in 4.14 with commit 891ef8dd2a8d14e4e73a81dcdb135b574c57f556 and fixed in 5.10.269 with commit 10fd1a8f58ac619a9e251f2858e2e2c8fd6cd667 Issue introduced in 4.14 with commit 891ef8dd2a8d14e4e73a81dcdb135b574c57f556 and fixed in 5.15.220 with commit eb0f422487228e140f3d609b032ac61aedcab8fa Issue introduced in 4.14 with commit 891ef8dd2a8d14e4e73a81dcdb135b574c57f556 and fixed in 6.1.187 with commit 9039e4f3e1c0ffe2b575b655b3f58fdd10f7e40c Issue introduced in 4.14 with commit 891ef8dd2a8d14e4e73a81dcdb135b574c57f556 and fixed in 6.6.156 with commit f52f1e75716d2ee49e013edf204ac92337c72fd8 Issue introduced in 4.14 with commit 891ef8dd2a8d14e4e73a81dcdb135b574c57f556 and fixed in 6.12.108 with commit 0e3f01fe2e704e76af4385b8a1742641885a191c Issue introduced in 4.14 with commit 891ef8dd2a8d14e4e73a81dcdb135b574c57f556 and fixed in 6.18.49 with commit 3e4476e58343fb8f2fffced9e22d935376b17aaf Issue introduced in 4.14 with commit 891ef8dd2a8d14e4e73a81dcdb135b574c57f556 and fixed in 7.1.13 with commit bf1c1151560d11036a144d917fa4c131831342d7 Issue introduced in 4.14 with commit 891ef8dd2a8d14e4e73a81dcdb135b574c57f556 and fixed in 7.2.3 with commit f4be3b391265e24c7720fc867c50062b436acf33 Issue introduced in 4.14 with commit 891ef8dd2a8d14e4e73a81dcdb135b574c57f556 and fixed in 7.3-rc1 with commit 44930446dde45a7a90fe1446fa38eb0e2c561646 Please see https://www.kernel.org for a full list of currently supported kernel versions by the kernel community. Unaffected versions might change over time as fixes are backported to older supported kernel versions. The official CVE entry at https://cve.org/CVERecord/?id=CVE-2026-80840 will be updated if fixes are backported, please check that for the most up to date information about this issue. Affected files ============== The file(s) affected by this issue are: net/ipv6/seg6_local.c Mitigation ========== The Linux kernel CVE team recommends that you update to the latest stable kernel version for this, and many other bugfixes. Individual changes are never tested alone, but rather are part of a larger kernel release. Cherry-picking individual commits is not recommended or supported by the Linux kernel community at all. If however, updating to the latest release is impossible, the individual changes to resolve this issue can be found at these commits: https://git.kernel.org/stable/c/10fd1a8f58ac619a9e251f2858e2e2c8fd6cd667 https://git.kernel.org/stable/c/eb0f422487228e140f3d609b032ac61aedcab8fa https://git.kernel.org/stable/c/9039e4f3e1c0ffe2b575b655b3f58fdd10f7e40c https://git.kernel.org/stable/c/f52f1e75716d2ee49e013edf204ac92337c72fd8 https://git.kernel.org/stable/c/0e3f01fe2e704e76af4385b8a1742641885a191c https://git.kernel.org/stable/c/3e4476e58343fb8f2fffced9e22d935376b17aaf https://git.kernel.org/stable/c/bf1c1151560d11036a144d917fa4c131831342d7 https://git.kernel.org/stable/c/f4be3b391265e24c7720fc867c50062b436acf33 https://git.kernel.org/stable/c/44930446dde45a7a90fe1446fa38eb0e2c561646