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CVE-2026-43037· NVD / CVE Program· CNA Linux

ip6_tunnel: clear skb2->cb[] in ip4ip6_err()

In the Linux kernel, the following vulnerability has been resolved: ip6_tunnel: clear skb2->cb[] in ip4ip6_err() Oskar Kjos reported the following problem. ip4ip6_err() calls icmp_send() on a cloned skb whose cb[] was written by the IPv6 receive path as struct inet6_skb_parm. icmp_send() passes IPCB(skb2) to __ip_options_echo(), which interprets that cb[] region as struct inet_skb_parm (IPv4). The layouts differ: inet6_skb_parm.nhoff at offset 14 overlaps inet_skb_parm.opt.rr, producing a non-zero rr value. __ip_options_echo() then reads optlen from attacker-controlled packet data at sptr[rr+1] and copies that many bytes into dopt->__data, a fixed 40-byte stack buffer (IP_OPTIONS_DATA_FIXED_SIZE). To fix this we clear skb2->cb[], as suggested by Oskar Kjos. Also add minimal IPv4 header validation (version == 4, ihl >= 5).

CriticalCVSS 9.8 · v3.1—No exploit Fix available
Published
May 1, 2026
Updated
Sep 1, 2026
EPSS
0.8% · 56th percentile
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JSON

Action score

39

Monitor

Low priority for now.

CVSS
39 / 40 · 9.8 / 10
CISA KEV
0 / 30 · Not listed
EPSS
0 / 30 · 0.8%

CNA vs NVD score

NVD
—
CNA · Linux
9.8
NVD has not scored this yet; the score shown is the CNA’s.

The score given by the assigning authority versus NVD’s independent score. A gap means the severity is contested.

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Affected systems

VendorProduct
linuxlinux kernel

Affected versions

NVD version ranges (for catalog products). Add the product to your stack with a version and matching uses these.

  • linux linux kernel2.6.22 and later · before 5.10.253
  • linux linux kernel5.11 and later · before 5.15.203
  • linux linux kernel5.16 and later · before 6.1.168
  • linux linux kernel6.2 and later · before 6.6.134
  • linux linux kernel6.7 and later · before 6.12.81
  • linux linux kernel6.13 and later · before 6.18.22
  • linux linux kernel6.19 and later · before 6.19.12
  • linux linux kernel7.0

Versions reported by the vendor

Affected version ranges reported by the assigning authority (Linux). Independent of NVD's CPE analysis and usually ahead of it.

  • Linux Linux

    • 2.6.22affected
    • c4d3efafcc933fd2ffd169d7dc4f980393a13796 and later · before ea9f65b27c8404e164848ebff1443310fd187629affected · git
    • c4d3efafcc933fd2ffd169d7dc4f980393a13796 and later · before d6621f60192fe10c047a4487be42a6f4c150707faffected · git
    • c4d3efafcc933fd2ffd169d7dc4f980393a13796 and later · before 2cc6e3b0fe0f0242d1f530a93a4924f48ab85ba5affected · git
    • c4d3efafcc933fd2ffd169d7dc4f980393a13796 and later · before a0c4ce9900a108eaf55d0f3b399cb55999647d39affected · git
    • c4d3efafcc933fd2ffd169d7dc4f980393a13796 and later · before 1063515ce15ff31065c4e7f8265f4c2fd3c54876affected · git
    • c4d3efafcc933fd2ffd169d7dc4f980393a13796 and later · before 590f622669b97eaf7b57a1de7b0a6e68c5d8b2c3affected · git
    • c4d3efafcc933fd2ffd169d7dc4f980393a13796 and later · before 4a622658f384b03560834cbe8ffcfe69a278f7c8affected · git
    • c4d3efafcc933fd2ffd169d7dc4f980393a13796 and later · before 2edfa31769a4add828a7e604b21cb82aaaa05925affected · git
    • before 2.6.22not affected · semver

Package-level exposure

OSV and GitHub Advisory data: ecosystem, package and range. SBOM matching uses this table.

EcosystemPackageAffected rangeFix
AlmaLinux:10kernelbefore 6.12.0-211.22.1.el10_26.12.0-211.22.1.el10_2
AlmaLinux:10kernel-64kbefore 6.12.0-211.22.1.el10_26.12.0-211.22.1.el10_2
AlmaLinux:10kernel-64k-corebefore 6.12.0-211.22.1.el10_26.12.0-211.22.1.el10_2
AlmaLinux:10kernel-64k-debugbefore 6.12.0-211.22.1.el10_26.12.0-211.22.1.el10_2
AlmaLinux:10kernel-64k-debug-corebefore 6.12.0-211.22.1.el10_26.12.0-211.22.1.el10_2
AlmaLinux:10kernel-64k-debug-develbefore 6.12.0-211.22.1.el10_26.12.0-211.22.1.el10_2
AlmaLinux:10kernel-64k-debug-devel-matchedbefore 6.12.0-211.22.1.el10_26.12.0-211.22.1.el10_2
AlmaLinux:10kernel-64k-debug-modulesbefore 6.12.0-211.22.1.el10_26.12.0-211.22.1.el10_2
AlmaLinux:10kernel-64k-debug-modules-corebefore 6.12.0-211.22.1.el10_26.12.0-211.22.1.el10_2
AlmaLinux:10kernel-64k-debug-modules-extrabefore 6.12.0-211.22.1.el10_26.12.0-211.22.1.el10_2
AlmaLinux:10kernel-64k-develbefore 6.12.0-211.22.1.el10_26.12.0-211.22.1.el10_2
AlmaLinux:10kernel-64k-devel-matchedbefore 6.12.0-211.22.1.el10_26.12.0-211.22.1.el10_2
AlmaLinux:10kernel-64k-modulesbefore 6.12.0-211.22.1.el10_26.12.0-211.22.1.el10_2
AlmaLinux:10kernel-64k-modules-corebefore 6.12.0-211.22.1.el10_26.12.0-211.22.1.el10_2
AlmaLinux:10kernel-64k-modules-extrabefore 6.12.0-211.22.1.el10_26.12.0-211.22.1.el10_2
AlmaLinux:10kernel-abi-stablelistsbefore 6.12.0-211.22.1.el10_26.12.0-211.22.1.el10_2
AlmaLinux:10kernel-corebefore 6.12.0-211.22.1.el10_26.12.0-211.22.1.el10_2
AlmaLinux:10kernel-cross-headersbefore 6.12.0-211.22.1.el10_26.12.0-211.22.1.el10_2
AlmaLinux:10kernel-debugbefore 6.12.0-211.22.1.el10_26.12.0-211.22.1.el10_2
AlmaLinux:10kernel-debug-corebefore 6.12.0-211.22.1.el10_26.12.0-211.22.1.el10_2
AlmaLinux:10kernel-debug-develbefore 6.12.0-211.22.1.el10_26.12.0-211.22.1.el10_2
AlmaLinux:10kernel-debug-devel-matchedbefore 6.12.0-211.22.1.el10_26.12.0-211.22.1.el10_2
AlmaLinux:10kernel-debug-modulesbefore 6.12.0-211.22.1.el10_26.12.0-211.22.1.el10_2
AlmaLinux:10kernel-debug-modules-corebefore 6.12.0-211.22.1.el10_26.12.0-211.22.1.el10_2

+96

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Remediation

Which version to upgrade to

Fix versions compiled from the vendor, package registries and Microsoft. Verify the vendor's note before upgrading.

Product / packageFixed versionSource
Linux Linux1063515ce15ff31065c4e7f8265f4c2fd3c54876Vendor (CNA)
Linux Linux2cc6e3b0fe0f0242d1f530a93a4924f48ab85ba5Vendor (CNA)
Linux Linux2edfa31769a4add828a7e604b21cb82aaaa05925Vendor (CNA)
Linux Linux4a622658f384b03560834cbe8ffcfe69a278f7c8Vendor (CNA)
Linux Linux590f622669b97eaf7b57a1de7b0a6e68c5d8b2c3Vendor (CNA)
Linux Linuxa0c4ce9900a108eaf55d0f3b399cb55999647d39Vendor (CNA)
Linux Linuxd6621f60192fe10c047a4487be42a6f4c150707fVendor (CNA)
Linux Linuxea9f65b27c8404e164848ebff1443310fd187629Vendor (CNA)
almalinux:bpftool4.18.0-553.132.1.el8_10 · AlmaLinux:8Package registry (OSV)
almalinux:kernel4.18.0-553.132.1.el8_10 · AlmaLinux:8Package registry (OSV)
almalinux:kernel-rt4.18.0-553.132.1.rt7.473.el8_10 · AlmaLinux:8Package registry (OSV)
almalinux:kernel-rt-core4.18.0-553.132.1.rt7.473.el8_10 · AlmaLinux:8Package registry (OSV)
almalinux:kernel-rt-debug4.18.0-553.132.1.rt7.473.el8_10 · AlmaLinux:8Package registry (OSV)
almalinux:kernel-rt-debug-core4.18.0-553.132.1.rt7.473.el8_10 · AlmaLinux:8Package registry (OSV)
almalinux:kernel-rt-debug-devel4.18.0-553.132.1.rt7.473.el8_10 · AlmaLinux:8Package registry (OSV)
almalinux:kernel-rt-debug-modules4.18.0-553.132.1.rt7.473.el8_10 · AlmaLinux:8Package registry (OSV)
almalinux:kernel-rt-debug-modules-extra4.18.0-553.132.1.rt7.473.el8_10 · AlmaLinux:8Package registry (OSV)
almalinux:kernel-rt-devel4.18.0-553.132.1.rt7.473.el8_10 · AlmaLinux:8Package registry (OSV)
almalinux:kernel-rt-modules4.18.0-553.132.1.rt7.473.el8_10 · AlmaLinux:8Package registry (OSV)
almalinux:kernel-rt-modules-extra4.18.0-553.132.1.rt7.473.el8_10 · AlmaLinux:8Package registry (OSV)
debian:linux6.1.170-1 · Debian:12Package registry (OSV)
red hat:kernel-rt0:5.14.0-284.174.1.rt14.459.el9_2 · Red Hat:rhel_e4s:9.2::nfvPackage registry (OSV)
red hat:kernel-rt-core0:5.14.0-284.174.1.rt14.459.el9_2 · Red Hat:rhel_e4s:9.2::nfvPackage registry (OSV)
red hat:kernel-rt-debug0:5.14.0-284.174.1.rt14.459.el9_2 · Red Hat:rhel_e4s:9.2::nfvPackage registry (OSV)
red hat:kernel-rt-debug-core0:5.14.0-284.174.1.rt14.459.el9_2 · Red Hat:rhel_e4s:9.2::nfvPackage registry (OSV)
red hat:kernel-rt-debug-debuginfo0:5.14.0-284.174.1.rt14.459.el9_2 · Red Hat:rhel_e4s:9.2::nfvPackage registry (OSV)
red hat:kernel-rt-debug-devel0:5.14.0-284.174.1.rt14.459.el9_2 · Red Hat:rhel_e4s:9.2::nfvPackage registry (OSV)
red hat:kernel-rt-debug-kvm0:5.14.0-284.174.1.rt14.459.el9_2 · Red Hat:rhel_e4s:9.2::nfvPackage registry (OSV)
red hat:kernel-rt-debug-modules0:5.14.0-284.174.1.rt14.459.el9_2 · Red Hat:rhel_e4s:9.2::nfvPackage registry (OSV)
red hat:kernel-rt-debug-modules-core0:5.14.0-284.174.1.rt14.459.el9_2 · Red Hat:rhel_e4s:9.2::nfvPackage registry (OSV)

+17

Exploit status

No known public exploit

No public exploit has been observed yet. That doesn't mean you're safe, only that the bar is a little higher.

Research context

For pentesters and researchers: attack profile, score disagreement, timeline, patch commits, credits, variant and chain candidates, bug bounty scope. All derived from existing data; no exploit code.

Timeline

From publication to today: proof of concept, Metasploit module, CISA KEV and fix record. Dates are as reported by the sources.

No dated events beyond publication.

EPSS, last 120 days

FIRST EPSS daily score; only changes of 0.01 or more are recorded (step chart).

Patch and commit links

Commit, PR and diff links among the references. A starting point for patch-diffing and variant hunting; fixes, not exploits.

No commit or PR link among the references.

Finders, reporters and analysts named in the CNA record. Click a name for that researcher’s other records.

No credits in the CNA record.

Variant candidates

Same product, same weakness class, within 18 months. If the patch missed the root cause, the sibling bug is here.

No nightly-computed relations.

Chain candidates

An authentication bypass and a privilege-requiring bug in the same product, published close together: combined they may become an unauthenticated path.

—

Bug bounty scope

No known public program.

Source: bounty-targets-data (public HackerOne, Bugcrowd, Intigriti, YesWeHack listings).

National notice (Türkiye Cybersecurity Directorate / USOM)

Official security notices citing this record; remediation advice is on the agency's page.

All national notices →

Technical details

Attack conditions

  • Anyone who can reach it over the internet can trigger it.
  • No account or password is required.
  • No user action is required.
  • No special conditions are required; it is repeatable.

If successful

Confidentiality
high · data can be read
Integrity
high · data or configuration can be modified
Availability
high · the service can be disrupted
Attack vector
Network
Attack complexity
Low
Privileges required
None
User interaction
None
Scope
Unchanged
Confidentiality impact
High
Integrity impact
High
Availability impact
High

Weakness class (CWE)

CWE-787 · Out-of-bounds Write

CVSS vector

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

nvd-secondary

Attack context

MITRE CAPEC attack patterns and ATT&CK techniques for this weakness class (CWE). A starting point for detection rules and threat hunting.

MITRE has no CAPEC/ATT&CK mapping for this CWE.

Change log

  1. Fix✗ → ✓

For records you follow, these changes also arrive as notifications. →

References

All records