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Fencer Vulns
high 7.8

CVE-2024-26804 json

net: ip_tunnel: prevent perpetual headroom growth

published 2024-04-04 2 y ago modified 2026-08-12 2 mo ago also EUVD-2024-24066

cvss
7.8
version 3.1, CNA
cisa kev
Not listed
not in CISA's catalog
epss
0.2%
EPSS 0.2% chance of exploitation in 30 days, percentile 16%
public exploits
0
none known

Summary

In the Linux kernel, the following vulnerability has been resolved:

net: ip_tunnel: prevent perpetual headroom growth

syzkaller triggered following kasan splat: BUG: KASAN: use-after-free in __skb_flow_dissect+0x19d1/0x7a50 net/core/flow_dissector.c:1170 Read of size 1 at addr ffff88812fb4000e by task syz-executor183/5191 [..] kasan_report+0xda/0x110 mm/kasan/report.c:588 __skb_flow_dissect+0x19d1/0x7a50 net/core/flow_dissector.c:1170 skb_flow_dissect_flow_keys include/linux/skbuff.h:1514 [inline] ___skb_get_hash net/core/flow_dissector.c:1791 [inline] __skb_get_hash+0xc7/0x540 net/core/flow_dissector.c:1856 skb_get_hash include/linux/skbuff.h:1556 [inline] ip_tunnel_xmit+0x1855/0x33c0 net/ipv4/ip_tunnel.c:748 ipip_tunnel_xmit+0x3cc/0x4e0 net/ipv4/ipip.c:308 __netdev_start_xmit include/linux/netdevice.h:4940 [inline] netdev_start_xmit include/linux/netdevice.h:4954 [inline] xmit_one net/core/dev.c:3548 [inline] dev_hard_start_xmit+0x13d/0x6d0 net/core/dev.c:3564 __dev_queue_xmit+0x7c1/0x3d60 net/core/dev.c:4349 dev_queue_xmit include/linux/netdevice.h:3134 [inline] neigh_connected_output+0x42c/0x5d0 net/core/neighbour.c:1592 ... ip_finish_output2+0x833/0x2550 net/ipv4/ip_output.c:235 ip_finish_output+0x31/0x310 net/ipv4/ip_output.c:323 .. iptunnel_xmit+0x5b4/0x9b0 net/ipv4/ip_tunnel_core.c:82 ip_tunnel_xmit+0x1dbc/0x33c0 net/ipv4/ip_tunnel.c:831 ipgre_xmit+0x4a1/0x980 net/ipv4/ip_gre.c:665 __netdev_start_xmit include/linux/netdevice.h:4940 [inline] netdev_start_xmit include/linux/netdevice.h:4954 [inline] xmit_one net/core/dev.c:3548 [inline] dev_hard_start_xmit+0x13d/0x6d0 net/core/dev.c:3564 ...

The splat occurs because skb->data points past skb->head allocated area. This is because neigh layer does: __skb_pull(skb, skb_network_offset(skb));

... but skb_network_offset() returns a negative offset and __skb_pull() arg is unsigned. IOW, we skb->data gets "adjusted" by a huge value.

The negative value is returned because skb->head and skb->data distance is more than 64k and skb->network_header (u16) has wrapped around.

The bug is in the ip_tunnel infrastructure, which can cause dev->needed_headroom to increment ad infinitum.

The syzkaller reproducer consists of packets getting routed via a gre tunnel, and route of gre encapsulated packets pointing at another (ipip) tunnel. The ipip encapsulation finds gre0 as next output device.

This results in the following pattern:

1). First packet is to be sent out via gre0. Route lookup found an output device, ipip0.

2). ip_tunnel_xmit for gre0 bumps gre0->needed_headroom based on the future output device, rt.dev->needed_headroom (ipip0).

3). ip output / start_xmit moves skb on to ipip0. which runs the same code path again (xmit recursion).

4). Routing step for the post-gre0-encap packet finds gre0 as output device to use for ipip0 encapsulated packet.

tunl0->needed_headroom is then incremented based on the (already bumped) gre0 device headroom.

This repeats for every future packet:

gre0->needed_headroom gets inflated because previous packets' ipip0 step incremented rt->dev (gre0) headroom, and ipip0 incremented because gre0 needed_headroom was increased.

For each subsequent packet, gre/ipip0->needed_headroom grows until post-expand-head reallocations result in a skb->head/data distance of more than 64k.

Once that happens, skb->network_header (u16) wraps around when pskb_expand_head tries to make sure that skb_network_offset() is unchanged after the headroom expansion/reallocation.

After this skb_network_offset(skb) returns a different (and negative) result post headroom expansion.

The next trip to neigh layer (or anything else that would __skb_pull the network header) makes skb->data point to a memory location outside skb->head area.

v2: Cap the needed_headroom update to an arbitarily chosen upperlimit to prevent perpetual increase instead of dropping the headroom increment completely.

Patch / fix

  • Linux Linux 2.6.34, 5.4.271, 5.10.212, 5.15.151, 6.1.81, 6.6.21, 6.7.9, 6.8
  • linux Debian 12 6.1.82-1
  • linux Debian 14, Debian 13 6.7.9-1

debian advisories DEBIAN-CVE-2024-26804

  • linux Ubuntu 20.04 LTS 5.4.0-186.206
  • linux Ubuntu 22.04 LTS 5.15.0-112.122
  • linux-aws Ubuntu 20.04 LTS 5.4.0-1126.136
  • linux-aws Ubuntu 22.04 LTS 5.15.0-1063.69
  • linux-gcp Ubuntu 20.04 LTS 5.4.0-1130.139
  • linux-gcp Ubuntu 22.04 LTS 5.15.0-1062.70
  • linux-gke Ubuntu 22.04 LTS 5.15.0-1060.66
  • linux-ibm Ubuntu 20.04 LTS 5.4.0-1073.78

ubuntu advisories UBUNTU-CVE-2024-26804

Ubuntu security data © Canonical Ltd., from https://github.com/canonical/ubuntu-security-notices via OSV; changed: normalised to fixed package versions per release. CC BY-SA 4.0

  • kernel RHEL 8 4.18.0-553.8.1.el8_10
  • perf RHEL 8 4.18.0-553.8.1.el8_10
  • bpftool RHEL 8 4.18.0-553.8.1.el8_10
  • kernel-core RHEL 8 4.18.0-553.8.1.el8_10
  • kernel-tools RHEL 8 4.18.0-553.8.1.el8_10
  • python3-perf RHEL 8 4.18.0-553.8.1.el8_10
  • kernel-modules RHEL 8 4.18.0-553.8.1.el8_10
  • kernel-zfcpdump RHEL 8 4.18.0-553.8.1.el8_10

red hat advisories RHSA-2024:4447RHSA-2024:4211RHSA-2024:4740RHSA-2024:4352RHSA-2024:3461RHSA-2024:3460

  • kernel-64kb SLES 15 SP5-LTSS, SLE High Performance Computing 15 SP5-LTSS, SLE High Performance Computing 15 SP5-ESPOS 5.14.21-150500.55.110.1
  • kernel-syms SLES for SAP 15 SP5, SLES 15 SP5-LTSS, SLE High Performance Computing 15 SP5-LTSS +1 more 5.14.21-150500.55.110.1
  • kernel-source SLES for SAP 15 SP5, SLES 15 SP5-LTSS, SLE Micro 5.5 +2 more 5.14.21-150500.55.110.1
  • kernel-default SLES for SAP 15 SP5, SLES 15 SP5-LTSS, SLE Micro 5.5 +3 more 5.14.21-150500.55.110.1
  • kernel-obs-build SLES for SAP 15 SP5, SLES 15 SP5-LTSS, SLE High Performance Computing 15 SP5-LTSS +1 more 5.14.21-150500.55.110.1
  • kernel-default-base SLES for SAP 15 SP5, SLES 15 SP5-LTSS, SLE Micro 5.5 +2 more 5.14.21-150500.55.110.1.150500.6.51.3
  • kernel-rt SLE Micro 5.5 5.14.21-150500.13.97.1
  • kernel-source-rt SLE Micro 5.5 5.14.21-150500.13.97.1

suse advisories SUSE-SU-2025:02173-1SUSE-SU-2025:01983-1SUSE-SU-2025:01966-1SUSE-SU-2025:20077-1SUSE-SU-2025:20073-1SUSE-SU-2025:0034-1

  • kernel-rt AlmaLinux 8 4.18.0-553.8.1.rt7.349.el8_10
  • kernel-rt-kvm AlmaLinux 8 4.18.0-553.8.1.rt7.349.el8_10
  • kernel-rt-core AlmaLinux 8 4.18.0-553.8.1.rt7.349.el8_10
  • kernel-rt-modules AlmaLinux 8 4.18.0-553.8.1.rt7.349.el8_10
  • kernel-rt-debug-kvm AlmaLinux 8 4.18.0-553.8.1.rt7.349.el8_10
  • kernel-rt-debug-core AlmaLinux 8 4.18.0-553.8.1.rt7.349.el8_10
  • kernel-rt-debug-modules AlmaLinux 8 4.18.0-553.8.1.rt7.349.el8_10
  • kernel-rt-modules-extra AlmaLinux 8 4.18.0-553.8.1.rt7.349.el8_10

almalinux advisories ALSA-2024:4352ALSA-2024:4211ALSA-2024:3306

  • kernel-rt Rocky Linux 8 4.18.0-553.8.1.rt7.349.el8_10
  • kernel Rocky Linux 8 4.18.0-553.8.1.el8_10

rocky linux advisories RLSA-2024:4352RLSA-2024:4211

Vendor advisories

What the vendors themselves say about their products: affected, fixed or not affected, and what to do.

red hat product security vex CVE-2024-26804 updated cvss 5.5

kernel: net: ip_tunnel: prevent perpetual headroom growth

  • Red Hat Enterprise Linux 6 perf, kernel, python-perf, kernel-kdump, kernel-firmware, kernel-bootwrapper, +1 more Red Hat Enterprise Linux 7 perf, kernel, bpftool, kernel-rt, python-perf, kernel-kdump, +8 more
    affected: no fix planned “Out of support scope”
  • Red Hat Enterprise Linux 9 kernel-rt, kernel-rt-kvm, kernel-rt-core, kernel-rt-modules, kernel-rt-debug-kvm, kernel-rt-debug-core, +12 more
    affected: no fix available
  • Red Hat CodeReady Linux Builder EUS (v.8.8) kernel-debuginfo-common-x86_64 4.18.0-477.64.1.el8_8, kernel-debuginfo-common-aarch64 4.18.0-477.64.1.el8_8, kernel-debuginfo-common-ppc64le 4.18.0-477.64.1.el8_8
    fixed: vendor fix RHSA-2024:4740
  • Red Hat CodeReady Linux Builder EUS (v.9.2) kernel-debuginfo-common-s390x 5.14.0-284.67.1.el9_2, kernel-debuginfo-common-x86_64 5.14.0-284.67.1.el9_2, kernel-debuginfo-common-aarch64 5.14.0-284.67.1.el9_2, kernel-debuginfo-common-ppc64le 5.14.0-284.67.1.el9_2
    fixed: vendor fix RHSA-2024:3461
  • Red Hat Enterprise Linux AppStream (v. 9) rv 5.14.0-427.18.1.el9_4, perf 5.14.0-427.18.1.el9_4, rtla 5.14.0-427.18.1.el9_4, kernel-devel-matched 5.14.0-427.18.1.el9_4, kernel-64k-devel-matched 5.14.0-427.18.1.el9_4, kernel-debug-devel-matched 5.14.0-427.18.1.el9_4, +6 more
    fixed: vendor fix RHSA-2024:3306
  • Red Hat Enterprise Linux AppStream EUS (v.9.2) perf 5.14.0-284.67.1.el9_2, rtla 5.14.0-284.67.1.el9_2, kernel-devel-matched 5.14.0-284.67.1.el9_2, kernel-64k-devel-matched 5.14.0-284.67.1.el9_2, kernel-debug-devel-matched 5.14.0-284.67.1.el9_2, kernel-debuginfo-common-s390x 5.14.0-284.67.1.el9_2, +5 more
    fixed: vendor fix RHSA-2024:3461
  • Red Hat Enterprise Linux BaseOS (v. 8) perf 4.18.0-553.8.1.el8_10, kernel 4.18.0-553.8.1.el8_10, bpftool 4.18.0-553.8.1.el8_10, kernel-core 4.18.0-553.8.1.el8_10, kernel-tools 4.18.0-553.8.1.el8_10, python3-perf 4.18.0-553.8.1.el8_10, +15 more
    fixed: vendor fix RHSA-2024:4211
  • Red Hat Enterprise Linux BaseOS (v. 9) bpftool 7.3.0-427.18.1.el9_4, kernel 5.14.0-427.18.1.el9_4, kernel-64k 5.14.0-427.18.1.el9_4, kernel-core 5.14.0-427.18.1.el9_4, kernel-tools 5.14.0-427.18.1.el9_4, python3-perf 5.14.0-427.18.1.el9_4, +28 more
    fixed: vendor fix RHSA-2024:3306
show 12 more
  • Red Hat Enterprise Linux BaseOS AUS (v.8.6) perf 4.18.0-372.111.1.el8_6, kernel 4.18.0-372.111.1.el8_6, bpftool 4.18.0-372.111.1.el8_6, kernel-core 4.18.0-372.111.1.el8_6, kernel-tools 4.18.0-372.111.1.el8_6, python3-perf 4.18.0-372.111.1.el8_6, +8 more Red Hat Enterprise Linux BaseOS E4S (v.8.6) perf 4.18.0-372.111.1.el8_6, kernel 4.18.0-372.111.1.el8_6, bpftool 4.18.0-372.111.1.el8_6, kernel-core 4.18.0-372.111.1.el8_6, kernel-tools 4.18.0-372.111.1.el8_6, python3-perf 4.18.0-372.111.1.el8_6, +15 more
    fixed: vendor fix RHSA-2024:4447
  • Red Hat Enterprise Linux BaseOS EUS (v.8.8) perf 4.18.0-477.64.1.el8_8, kernel 4.18.0-477.64.1.el8_8, bpftool 4.18.0-477.64.1.el8_8, kernel-core 4.18.0-477.64.1.el8_8, kernel-tools 4.18.0-477.64.1.el8_8, python3-perf 4.18.0-477.64.1.el8_8, +15 more
    fixed: vendor fix RHSA-2024:4740
  • Red Hat Enterprise Linux BaseOS EUS (v.9.2) bpftool 7.0.0-284.67.1.el9_2, kernel 5.14.0-284.67.1.el9_2, kernel-64k 5.14.0-284.67.1.el9_2, kernel-core 5.14.0-284.67.1.el9_2, kernel-tools 5.14.0-284.67.1.el9_2, python3-perf 5.14.0-284.67.1.el9_2, +28 more
    fixed: vendor fix RHSA-2024:3461
  • Red Hat Enterprise Linux BaseOS TUS (v.8.6) perf 4.18.0-372.111.1.el8_6, kernel 4.18.0-372.111.1.el8_6, bpftool 4.18.0-372.111.1.el8_6, kernel-core 4.18.0-372.111.1.el8_6, kernel-tools 4.18.0-372.111.1.el8_6, python3-perf 4.18.0-372.111.1.el8_6, +8 more
    fixed: vendor fix RHSA-2024:4447
  • Red Hat Enterprise Linux CRB (v. 8) kernel-debuginfo-common-x86_64 4.18.0-553.8.1.el8_10, kernel-debuginfo-common-aarch64 4.18.0-553.8.1.el8_10, kernel-debuginfo-common-ppc64le 4.18.0-553.8.1.el8_10
    fixed: vendor fix RHSA-2024:4211
  • Red Hat Enterprise Linux CRB (v. 9) libperf 5.14.0-427.18.1.el9_4, kernel-debuginfo-common-s390x 5.14.0-427.18.1.el9_4, kernel-debuginfo-common-x86_64 5.14.0-427.18.1.el9_4, kernel-debuginfo-common-aarch64 5.14.0-427.18.1.el9_4, kernel-debuginfo-common-ppc64le 5.14.0-427.18.1.el9_4
    fixed: vendor fix RHSA-2024:3306
  • Red Hat Enterprise Linux NFV (v. 8) kernel-rt 4.18.0-553.8.1.rt7.349.el8_10, kernel-rt-kvm 4.18.0-553.8.1.rt7.349.el8_10, kernel-rt-core 4.18.0-553.8.1.rt7.349.el8_10, kernel-rt-modules 4.18.0-553.8.1.rt7.349.el8_10, kernel-rt-debug-kvm 4.18.0-553.8.1.rt7.349.el8_10, kernel-rt-debug-core 4.18.0-553.8.1.rt7.349.el8_10, +4 more
    fixed: vendor fix RHSA-2024:4352
  • Red Hat Enterprise Linux NFV (v. 9) kernel-rt 5.14.0-427.18.1.el9_4, kernel-rt-kvm 5.14.0-427.18.1.el9_4, kernel-rt-core 5.14.0-427.18.1.el9_4, kernel-rt-modules 5.14.0-427.18.1.el9_4, kernel-rt-debug-kvm 5.14.0-427.18.1.el9_4, kernel-rt-debug-core 5.14.0-427.18.1.el9_4, +6 more
    fixed: vendor fix RHSA-2024:3306
  • Red Hat Enterprise Linux Real Time EUS (v.9.2) kernel-rt 5.14.0-284.67.1.rt14.352.el9_2, kernel-rt-core 5.14.0-284.67.1.rt14.352.el9_2, kernel-rt-modules 5.14.0-284.67.1.rt14.352.el9_2, kernel-rt-debug-core 5.14.0-284.67.1.rt14.352.el9_2, kernel-rt-modules-core 5.14.0-284.67.1.rt14.352.el9_2, kernel-rt-debug-modules 5.14.0-284.67.1.rt14.352.el9_2, +4 more Red Hat Enterprise Linux Real Time for NFV EUS (v.9.2) kernel-rt 5.14.0-284.67.1.rt14.352.el9_2, kernel-rt-kvm 5.14.0-284.67.1.rt14.352.el9_2, kernel-rt-core 5.14.0-284.67.1.rt14.352.el9_2, kernel-rt-modules 5.14.0-284.67.1.rt14.352.el9_2, kernel-rt-debug-kvm 5.14.0-284.67.1.rt14.352.el9_2, kernel-rt-debug-core 5.14.0-284.67.1.rt14.352.el9_2, +6 more
    fixed: vendor fix RHSA-2024:3460
  • Red Hat Enterprise Linux RT (v. 8) kernel-rt 4.18.0-553.8.1.rt7.349.el8_10, kernel-rt-core 4.18.0-553.8.1.rt7.349.el8_10, kernel-rt-modules 4.18.0-553.8.1.rt7.349.el8_10, kernel-rt-debug-core 4.18.0-553.8.1.rt7.349.el8_10, kernel-rt-debug-modules 4.18.0-553.8.1.rt7.349.el8_10, kernel-rt-modules-extra 4.18.0-553.8.1.rt7.349.el8_10, +2 more
    fixed: vendor fix RHSA-2024:4352
  • Red Hat Enterprise Linux RT (v. 9) kernel-rt 5.14.0-427.18.1.el9_4, kernel-rt-core 5.14.0-427.18.1.el9_4, kernel-rt-modules 5.14.0-427.18.1.el9_4, kernel-rt-debug-core 5.14.0-427.18.1.el9_4, kernel-rt-modules-core 5.14.0-427.18.1.el9_4, kernel-rt-debug-modules 5.14.0-427.18.1.el9_4, +4 more
    fixed: vendor fix RHSA-2024:3306
  • Red Hat Enterprise Linux AppStream EUS (v.9.2) kernel-doc 5.14.0-284.67.1.el9_2 Red Hat Enterprise Linux BaseOS (v. 8) kernel-headers 4.18.0-553.8.1.el8_10, kernel-cross-headers 4.18.0-553.8.1.el8_10
    not affected: vulnerable code not present

Red Hat CSAF VEX © Red Hat, Inc., from https://security.access.redhat.com/data/csaf/v2/vex/; changed: reduced to product statuses and remediations. CC BY 4.0 · csaf

cisa ICSA-25-226-15 updated

Siemens SINEC OS

  • Siemens RUGGEDCOM RST2428P (6GK6242-6PA00) Siemens SCALANCE XC-300/XR-300/XC-400/XR-500WG/XR-500 family Siemens SCALANCE XCM-/XRM-/XCH-/XRH-300 family
    not affected

Facts from CISA's republication of the vendor's own advisory (CSAF); the linked advisory is the authoritative source. CISA notification · csaf

CISA SSVC

Exploitation
none
Automatable
no
Technical impact
total
Assessed
2 mo ago

Exploit prediction

0.25% chance of exploitation in the next 30 days, higher than 16% of all scored CVEs (FIRST EPSS, 2026-11-08).

CVSS scores

assigned by version score vector
CNA 3.1 7.8 CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H

Affected products

  • Linux Linux

Classification

Weakness
Technology feeds

References

Sources

Fencer Vulns keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.