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Fencer Vulns
high 8.8

CVE-2024-27415 json

netfilter: bridge: confirm multicast packets before passing them up the stack

published 2024-05-17 2 y ago modified 2026-08-05 3 mo ago also EUVD-2024-24619

cvss
8.8
version 3.1, CNA
cisa kev
Not listed
not in CISA's catalog
epss
0.3%
EPSS 0.3% chance of exploitation in 30 days, percentile 16%
public exploits
0
none known

Summary

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

netfilter: bridge: confirm multicast packets before passing them up the stack

conntrack nf_confirm logic cannot handle cloned skbs referencing the same nf_conn entry, which will happen for multicast (broadcast) frames on bridges.

Example: macvlan0 | br0 / \ ethX ethY

ethX (or Y) receives a L2 multicast or broadcast packet containing an IP packet, flow is not yet in conntrack table.

1. skb passes through bridge and fake-ip (br_netfilter)Prerouting. -> skb->_nfct now references a unconfirmed entry 2. skb is broad/mcast packet. bridge now passes clones out on each bridge interface. 3. skb gets passed up the stack. 4. In macvlan case, macvlan driver retains clone(s) of the mcast skb and schedules a work queue to send them out on the lower devices.

The clone skb->_nfct is not a copy, it is the same entry as the original skb. The macvlan rx handler then returns RX_HANDLER_PASS. 5. Normal conntrack hooks (in NF_INET_LOCAL_IN) confirm the orig skb.

The Macvlan broadcast worker and normal confirm path will race.

This race will not happen if step 2 already confirmed a clone. In that case later steps perform skb_clone() with skb->_nfct already confirmed (in hash table). This works fine.

But such confirmation won't happen when eb/ip/nftables rules dropped the packets before they reached the nf_confirm step in postrouting.

Pablo points out that nf_conntrack_bridge doesn't allow use of stateful nat, so we can safely discard the nf_conn entry and let inet call conntrack again.

This doesn't work for bridge netfilter: skb could have a nat transformation. Also bridge nf prevents re-invocation of inet prerouting via 'sabotage_in' hook.

Work around this problem by explicit confirmation of the entry at LOCAL_IN time, before upper layer has a chance to clone the unconfirmed entry.

The downside is that this disables NAT and conntrack helpers.

Alternative fix would be to add locking to all code parts that deal with unconfirmed packets, but even if that could be done in a sane way this opens up other problems, for example:

-m physdev --physdev-out eth0 -j SNAT --snat-to 1.2.3.4 -m physdev --physdev-out eth1 -j SNAT --snat-to 1.2.3.5

For multicast case, only one of such conflicting mappings will be created, conntrack only handles 1:1 NAT mappings.

Users should set create a setup that explicitly marks such traffic NOTRACK (conntrack bypass) to avoid this, but we cannot auto-bypass them, ruleset might have accept rules for untracked traffic already, so user-visible behaviour would change.

Patch / fix

  • Linux Linux 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-2024-27415

  • linux Ubuntu 22.04 LTS 5.15.0-112.122
  • linux-aws Ubuntu 22.04 LTS 5.15.0-1063.69
  • 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 22.04 LTS 5.15.0-1056.59
  • linux-kvm Ubuntu 22.04 LTS 5.15.0-1060.65
  • linux-azure Ubuntu 22.04 LTS 5.15.0-1066.75
  • linux-gkeop Ubuntu 22.04 LTS 5.15.0-1046.53

ubuntu advisories UBUNTU-CVE-2024-27415

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 9 5.14.0-427.33.1.el9_4
  • rv RHEL 9 5.14.0-427.33.1.el9_4
  • perf RHEL 9 5.14.0-427.33.1.el9_4
  • rtla RHEL 9 5.14.0-427.33.1.el9_4
  • bpftool RHEL 9 7.3.0-427.33.1.el9_4
  • libperf RHEL 9 5.14.0-427.33.1.el9_4
  • kernel-rt RHEL 9 5.14.0-427.33.1.el9_4
  • kernel-64k RHEL 9 5.14.0-427.33.1.el9_4

red hat advisories RHSA-2024:7490RHSA-2024:7489RHSA-2024:5928

  • kernel-rt Real Time Module 15 SP7 6.4.0-150700.7.3.1
  • kernel-syms-rt Real Time Module 15 SP7 6.4.0-150700.7.3.1
  • kernel-rt_debug Real Time Module 15 SP7 6.4.0-150700.7.3.1
  • kernel-source-rt Real Time Module 15 SP7 6.4.0-150700.7.3.1
  • kernel-azure SLE Module for Public Cloud 15 SP7 6.4.0-150700.20.3.1
  • kernel-syms-azure SLE Module for Public Cloud 15 SP7 6.4.0-150700.20.3.1
  • kernel-source-azure SLE Module for Public Cloud 15 SP7 6.4.0-150700.20.3.1
  • kernel-rt Real Time Module 15 SP6, openSUSE Leap 15.6 6.4.0-150600.10.39.1

suse advisories SUSE-SU-2025:01972-1SUSE-SU-2025:01967-1SUSE-SU-2025:01964-1SUSE-SU-2025:01951-1SUSE-SU-2025:01919-1SUSE-SU-2025:01707-1

  • kernel AlmaLinux 9 5.14.0-427.33.1.el9_4
  • rv AlmaLinux 9 5.14.0-427.33.1.el9_4
  • perf AlmaLinux 9 5.14.0-427.33.1.el9_4
  • rtla AlmaLinux 9 5.14.0-427.33.1.el9_4
  • bpftool AlmaLinux 9 7.3.0-427.33.1.el9_4
  • libperf AlmaLinux 9 5.14.0-427.33.1.el9_4
  • kernel-rt AlmaLinux 9 5.14.0-427.33.1.el9_4
  • kernel-64k AlmaLinux 9 5.14.0-427.33.1.el9_4

almalinux advisories ALSA-2024:5928

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-2024-27415 updated cvss 5.5

kernel: netfilter: bridge: confirm multicast packets before passing them up the stack

  • 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 8 perf, kernel, bpftool, kernel-rt, kernel-core, kernel-tools, +29 more
    affected: no fix planned “Will not fix”
  • 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.9.2) kernel-debuginfo-common-s390x 5.14.0-284.86.1.el9_2, kernel-debuginfo-common-x86_64 5.14.0-284.86.1.el9_2, kernel-debuginfo-common-aarch64 5.14.0-284.86.1.el9_2, kernel-debuginfo-common-ppc64le 5.14.0-284.86.1.el9_2
    fixed: vendor fix RHSA-2024:7489
  • Red Hat Enterprise Linux AppStream (v. 9) rv 5.14.0-427.33.1.el9_4, perf 5.14.0-427.33.1.el9_4, rtla 5.14.0-427.33.1.el9_4, kernel-devel-matched 5.14.0-427.33.1.el9_4, kernel-64k-devel-matched 5.14.0-427.33.1.el9_4, kernel-debug-devel-matched 5.14.0-427.33.1.el9_4, +6 more
    fixed: vendor fix RHSA-2024:5928
  • Red Hat Enterprise Linux AppStream EUS (v.9.2) perf 5.14.0-284.86.1.el9_2, rtla 5.14.0-284.86.1.el9_2, kernel-devel-matched 5.14.0-284.86.1.el9_2, kernel-64k-devel-matched 5.14.0-284.86.1.el9_2, kernel-debug-devel-matched 5.14.0-284.86.1.el9_2, kernel-debuginfo-common-s390x 5.14.0-284.86.1.el9_2, +5 more
    fixed: vendor fix RHSA-2024:7489
  • Red Hat Enterprise Linux BaseOS (v. 9) bpftool 7.3.0-427.33.1.el9_4, kernel 5.14.0-427.33.1.el9_4, kernel-64k 5.14.0-427.33.1.el9_4, kernel-core 5.14.0-427.33.1.el9_4, kernel-tools 5.14.0-427.33.1.el9_4, python3-perf 5.14.0-427.33.1.el9_4, +28 more
    fixed: vendor fix RHSA-2024:5928
  • Red Hat Enterprise Linux BaseOS EUS (v.9.2) bpftool 7.0.0-284.86.1.el9_2, kernel 5.14.0-284.86.1.el9_2, kernel-64k 5.14.0-284.86.1.el9_2, kernel-core 5.14.0-284.86.1.el9_2, kernel-tools 5.14.0-284.86.1.el9_2, python3-perf 5.14.0-284.86.1.el9_2, +28 more
    fixed: vendor fix RHSA-2024:7489
show 4 more
  • Red Hat Enterprise Linux CRB (v. 9) libperf 5.14.0-427.33.1.el9_4, kernel-debuginfo-common-s390x 5.14.0-427.33.1.el9_4, kernel-debuginfo-common-x86_64 5.14.0-427.33.1.el9_4, kernel-debuginfo-common-aarch64 5.14.0-427.33.1.el9_4, kernel-debuginfo-common-ppc64le 5.14.0-427.33.1.el9_4 Red Hat Enterprise Linux NFV (v. 9) kernel-rt 5.14.0-427.33.1.el9_4, kernel-rt-kvm 5.14.0-427.33.1.el9_4, kernel-rt-core 5.14.0-427.33.1.el9_4, kernel-rt-modules 5.14.0-427.33.1.el9_4, kernel-rt-debug-kvm 5.14.0-427.33.1.el9_4, kernel-rt-debug-core 5.14.0-427.33.1.el9_4, +6 more
    fixed: vendor fix RHSA-2024:5928
  • Red Hat Enterprise Linux Real Time EUS (v.9.2) kernel-rt 5.14.0-284.86.1.rt14.371.el9_2, kernel-rt-core 5.14.0-284.86.1.rt14.371.el9_2, kernel-rt-modules 5.14.0-284.86.1.rt14.371.el9_2, kernel-rt-debug-core 5.14.0-284.86.1.rt14.371.el9_2, kernel-rt-modules-core 5.14.0-284.86.1.rt14.371.el9_2, kernel-rt-debug-modules 5.14.0-284.86.1.rt14.371.el9_2, +4 more Red Hat Enterprise Linux Real Time for NFV EUS (v.9.2) kernel-rt 5.14.0-284.86.1.rt14.371.el9_2, kernel-rt-kvm 5.14.0-284.86.1.rt14.371.el9_2, kernel-rt-core 5.14.0-284.86.1.rt14.371.el9_2, kernel-rt-modules 5.14.0-284.86.1.rt14.371.el9_2, kernel-rt-debug-kvm 5.14.0-284.86.1.rt14.371.el9_2, kernel-rt-debug-core 5.14.0-284.86.1.rt14.371.el9_2, +6 more
    fixed: vendor fix RHSA-2024:7490
  • Red Hat Enterprise Linux RT (v. 9) kernel-rt 5.14.0-427.33.1.el9_4, kernel-rt-core 5.14.0-427.33.1.el9_4, kernel-rt-modules 5.14.0-427.33.1.el9_4, kernel-rt-debug-core 5.14.0-427.33.1.el9_4, kernel-rt-modules-core 5.14.0-427.33.1.el9_4, kernel-rt-debug-modules 5.14.0-427.33.1.el9_4, +4 more
    fixed: vendor fix RHSA-2024:5928
  • Red Hat Enterprise Linux AppStream EUS (v.9.2) kernel-doc 5.14.0-284.86.1.el9_2
    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 SSVC

Exploitation
none
Automatable
no
Technical impact
partial
Assessed
2 y 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 8.8 CVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
NVD 3.1 4.7 CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H

Affected products

  • Linux Linux

Classification

Weakness
  • CWE-362 Concurrent Execution using Shared Resource with Improper Synchronization
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.