CVE-2026-43037: ip6_tunnel: clear skb2->cb[] in ip4ip6_err()
Noroxi assessment
Priority: Monitor (action score 39/100)
- The sources we track (CISA KEV, Exploit-DB, Metasploit, Nuclei, GitHub) show no public exploit code or exploitation in the wild.
- Probability of exploitation in the next 30 days: 0.68% (FIRST EPSS); higher than 52.9% of all records.
- 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.
- According to CISA the attack is automatable: targets can be found by mass scanning.
- Fixed version: Linux Linux 1063515ce15ff31065c4e7f8265f4c2fd3c54876, 2cc6e3b0fe0f0242d1f530a93a4924f48ab85ba5, 2edfa31769a4add828a7e604b21cb82aaaa05925; cbl2 kernel 5.15.202.1-1 on CBL-Mariner 2.0 Release Notes.
- Mentioned 1 time in Turkish national cyber security advisories (siberguvenlik.gov.tr).
Low priority for now. Upgrade to Linux Linux 1063515ce15ff31065c4e7f8265f4c2fd3c54876, 2cc6e3b0fe0f0242d1f530a93a4924f48ab85ba5, 2edfa31769a4add828a7e604b21cb82aaaa05925; cbl2 kernel 5.15.202.1-1 on CBL-Mariner 2.0 Release Notes or later.
Generated automatically from the record's data: CVSS (NVD and CNA), CISA KEV and SSVC, FIRST EPSS, exploit sources, fixed versions. How we calculate it
Primary sources: NVD · CVE.org · FIRST EPSS
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).
- BDU:2026-07832
- ALSA-2026:25120
- ALSA-2026:25121
- ALSA-2026:25191
- ALSA-2026:25217
- RHSA-2026:22900
- RHSA-2026:22940
- RHSA-2026:22964
- RHSA-2026:23224
- RHSA-2026:23237
- RHSA-2026:24343
- RHSA-2026:25120
- RHSA-2026:25121
- RHSA-2026:25191
- RHSA-2026:25217
- RHSA-2026:25533
- RHSA-2026:25534
- RHSA-2026:26535
- RHSA-2026:27719
- RHSA-2026:27729
- Published
- May 1, 2026
- Updated
- Oct 19, 2026
- EPSS
- 0.6% · 52th percentile
- CWE
- CWE-787
Report tools
Action score
39
Monitor
Low priority for now.
- CVSS
- 39 / 40 · 9.8 / 10
- CISA KEV
- 0 / 30 · Not listed
- EPSS
- 0 / 30 · 0.6%
CISA SSVC decision
- Exploitation
- none
- Automatable
- yes
- Technical impact
- total
Vulnrichment: CISA's decision-tree inputs.
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.
Get told when this record changes
- Not in KEV: no record of exploitation in the wild
- No public exploit code on record
- A fix has been released
If any of these changes, we'll tell you in the daily email digest.
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Noroxi analysis
What does it mean in your environment?
The assessment above is generated automatically from the record's data; it doesn't know your environment. Our team verifies on your systems whether this vulnerability is actually exploitable and which mitigation is enough.
We use this product, ask for helpAffected systems
Is your version affected?
Pick the product and type the version you run. It's compared with this record's version ranges in your browser; the version isn't sent anywhere.
| Vendor | Product | CPE |
|---|---|---|
| linux | linux kernel | cpe:2.3:o:linux:linux_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.
| Ecosystem | Package | Affected range | Fix |
|---|---|---|---|
| AlmaLinux:10 | kernel | before 6.12.0-211.22.1.el10_2 | 6.12.0-211.22.1.el10_2 |
| AlmaLinux:10 | kernel-64k | before 6.12.0-211.22.1.el10_2 | 6.12.0-211.22.1.el10_2 |
| AlmaLinux:10 | kernel-64k-core | before 6.12.0-211.22.1.el10_2 | 6.12.0-211.22.1.el10_2 |
| AlmaLinux:10 | kernel-64k-debug | before 6.12.0-211.22.1.el10_2 | 6.12.0-211.22.1.el10_2 |
| AlmaLinux:10 | kernel-64k-debug-core | before 6.12.0-211.22.1.el10_2 | 6.12.0-211.22.1.el10_2 |
| AlmaLinux:10 | kernel-64k-debug-devel | before 6.12.0-211.22.1.el10_2 | 6.12.0-211.22.1.el10_2 |
| AlmaLinux:10 | kernel-64k-debug-devel-matched | before 6.12.0-211.22.1.el10_2 | 6.12.0-211.22.1.el10_2 |
| AlmaLinux:10 | kernel-64k-debug-modules | before 6.12.0-211.22.1.el10_2 | 6.12.0-211.22.1.el10_2 |
| AlmaLinux:10 | kernel-64k-debug-modules-core | before 6.12.0-211.22.1.el10_2 | 6.12.0-211.22.1.el10_2 |
| AlmaLinux:10 | kernel-64k-debug-modules-extra | before 6.12.0-211.22.1.el10_2 | 6.12.0-211.22.1.el10_2 |
| AlmaLinux:10 | kernel-64k-devel | before 6.12.0-211.22.1.el10_2 | 6.12.0-211.22.1.el10_2 |
| AlmaLinux:10 | kernel-64k-devel-matched | before 6.12.0-211.22.1.el10_2 | 6.12.0-211.22.1.el10_2 |
| AlmaLinux:10 | kernel-64k-modules | before 6.12.0-211.22.1.el10_2 | 6.12.0-211.22.1.el10_2 |
| AlmaLinux:10 | kernel-64k-modules-core | before 6.12.0-211.22.1.el10_2 | 6.12.0-211.22.1.el10_2 |
| AlmaLinux:10 | kernel-64k-modules-extra | before 6.12.0-211.22.1.el10_2 | 6.12.0-211.22.1.el10_2 |
| AlmaLinux:10 | kernel-abi-stablelists | before 6.12.0-211.22.1.el10_2 | 6.12.0-211.22.1.el10_2 |
| AlmaLinux:10 | kernel-core | before 6.12.0-211.22.1.el10_2 | 6.12.0-211.22.1.el10_2 |
| AlmaLinux:10 | kernel-cross-headers | before 6.12.0-211.22.1.el10_2 | 6.12.0-211.22.1.el10_2 |
| AlmaLinux:10 | kernel-debug | before 6.12.0-211.22.1.el10_2 | 6.12.0-211.22.1.el10_2 |
| AlmaLinux:10 | kernel-debug-core | before 6.12.0-211.22.1.el10_2 | 6.12.0-211.22.1.el10_2 |
| AlmaLinux:10 | kernel-debug-devel | before 6.12.0-211.22.1.el10_2 | 6.12.0-211.22.1.el10_2 |
| AlmaLinux:10 | kernel-debug-devel-matched | before 6.12.0-211.22.1.el10_2 | 6.12.0-211.22.1.el10_2 |
| AlmaLinux:10 | kernel-debug-modules | before 6.12.0-211.22.1.el10_2 | 6.12.0-211.22.1.el10_2 |
| AlmaLinux:10 | kernel-debug-modules-core | before 6.12.0-211.22.1.el10_2 | 6.12.0-211.22.1.el10_2 |
+96
Same product
linux: all recordsOther highest-scoring records for the same primary product.
- CVE-2026-31431crypto: algif_aead - Revert to operating out-of-placeKEV90Now
- CVE-2022-0847A flaw was found in the way the "flags" member of the new pipe buffer structure was lacking proper initialization in copy_page_to_iter_pipe KEV89Now
- CVE-2021-22555Heap Out-Of-Bounds Write in Netfilter IP6T_SO_SET_REPLACEKEV85Now
Published before and after this one in the same product
- ← EarlierCVE-2026-43035May 1, 2026 · net: sched: cls_api: fix tc_chain_fill_node to initialize tcm_info to zero to prevent an info-leak22Monitor
- ← EarlierCVE-2026-43036May 1, 2026 · net: use skb_header_pointer() for TCPv4 GSO frag_off check22Monitor
- Later →CVE-2026-43038May 1, 2026 · ipv6: icmp: clear skb2->cb[] in ip6_err_gen_icmpv6_unreach()39Monitor
Remediation
Which version to upgrade to
Fix versions compiled from the vendor, package registries and Microsoft. Verify the vendor's note before upgrading.
| Product / package | Fixed version | Source |
|---|---|---|
| Linux Linux | 1063515ce15ff31065c4e7f8265f4c2fd3c54876 | Vendor (CNA) |
| Linux Linux | 2cc6e3b0fe0f0242d1f530a93a4924f48ab85ba5 | Vendor (CNA) |
| Linux Linux | 2edfa31769a4add828a7e604b21cb82aaaa05925 | Vendor (CNA) |
| Linux Linux | 4a622658f384b03560834cbe8ffcfe69a278f7c8 | Vendor (CNA) |
| Linux Linux | 590f622669b97eaf7b57a1de7b0a6e68c5d8b2c3 | Vendor (CNA) |
| Linux Linux | a0c4ce9900a108eaf55d0f3b399cb55999647d39 | Vendor (CNA) |
| Linux Linux | d6621f60192fe10c047a4487be42a6f4c150707f | Vendor (CNA) |
| Linux Linux | ea9f65b27c8404e164848ebff1443310fd187629 | Vendor (CNA) |
| cbl2 kernel 5.15.202.1-1 on CBL-Mariner 2.0 | Release Notes | Microsoft (MSRC) |
| almalinux:bpftool | 4.18.0-553.132.1.el8_10 · AlmaLinux:8 | Package registry (OSV) |
| almalinux:kernel | 4.18.0-553.132.1.el8_10 · AlmaLinux:8 | Package registry (OSV) |
| almalinux:kernel-rt | 4.18.0-553.132.1.rt7.473.el8_10 · AlmaLinux:8 | Package registry (OSV) |
| almalinux:kernel-rt-core | 4.18.0-553.132.1.rt7.473.el8_10 · AlmaLinux:8 | Package registry (OSV) |
| almalinux:kernel-rt-debug | 4.18.0-553.132.1.rt7.473.el8_10 · AlmaLinux:8 | Package registry (OSV) |
| almalinux:kernel-rt-debug-core | 4.18.0-553.132.1.rt7.473.el8_10 · AlmaLinux:8 | Package registry (OSV) |
| almalinux:kernel-rt-debug-devel | 4.18.0-553.132.1.rt7.473.el8_10 · AlmaLinux:8 | Package registry (OSV) |
| almalinux:kernel-rt-debug-modules | 4.18.0-553.132.1.rt7.473.el8_10 · AlmaLinux:8 | Package registry (OSV) |
| almalinux:kernel-rt-debug-modules-extra | 4.18.0-553.132.1.rt7.473.el8_10 · AlmaLinux:8 | Package registry (OSV) |
| almalinux:kernel-rt-devel | 4.18.0-553.132.1.rt7.473.el8_10 · AlmaLinux:8 | Package registry (OSV) |
| almalinux:kernel-rt-modules | 4.18.0-553.132.1.rt7.473.el8_10 · AlmaLinux:8 | Package registry (OSV) |
| almalinux:kernel-rt-modules-extra | 4.18.0-553.132.1.rt7.473.el8_10 · AlmaLinux:8 | Package registry (OSV) |
| debian:linux | 6.1.170-1 · Debian:12 | Package registry (OSV) |
| red hat:kernel-rt | 0:5.14.0-284.174.1.rt14.459.el9_2 · Red Hat:rhel_e4s:9.2::nfv | Package registry (OSV) |
| red hat:kernel-rt-core | 0:5.14.0-284.174.1.rt14.459.el9_2 · Red Hat:rhel_e4s:9.2::nfv | Package registry (OSV) |
| red hat:kernel-rt-debug | 0:5.14.0-284.174.1.rt14.459.el9_2 · Red Hat:rhel_e4s:9.2::nfv | Package registry (OSV) |
| red hat:kernel-rt-debug-core | 0:5.14.0-284.174.1.rt14.459.el9_2 · Red Hat:rhel_e4s:9.2::nfv | Package registry (OSV) |
| red hat:kernel-rt-debug-debuginfo | 0:5.14.0-284.174.1.rt14.459.el9_2 · Red Hat:rhel_e4s:9.2::nfv | Package registry (OSV) |
| red hat:kernel-rt-debug-devel | 0:5.14.0-284.174.1.rt14.459.el9_2 · Red Hat:rhel_e4s:9.2::nfv | Package registry (OSV) |
| red hat:kernel-rt-debug-kvm | 0:5.14.0-284.174.1.rt14.459.el9_2 · Red Hat:rhel_e4s:9.2::nfv | Package registry (OSV) |
| red hat:kernel-rt-debug-modules | 0:5.14.0-284.174.1.rt14.459.el9_2 · Red Hat:rhel_e4s:9.2::nfv | Package registry (OSV) |
+18
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.
No history yet (it accumulates with the daily EPSS job).
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.
Credits
All researchersFinders, 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.
- TR-26-0143 · May 4, 2026(Linux Kernel Güvenlik Bildirimi)
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 WriteCVSS 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
- SSVC exploitation— → none
- Fix✗ → ✓
For records you follow, these changes also arrive as notifications. →
References
Show all references (19 more)Show less
- git.kernel.org/stable/c/2cc6e3b0fe0f0242d1f530a93a4924f48ab85ba5
- git.kernel.org/stable/c/2edfa31769a4add828a7e604b21cb82aaaa05925
- git.kernel.org/stable/c/4a622658f384b03560834cbe8ffcfe69a278f7c8
- git.kernel.org/stable/c/590f622669b97eaf7b57a1de7b0a6e68c5d8b2c3
- git.kernel.org/stable/c/a0c4ce9900a108eaf55d0f3b399cb55999647d39
- git.kernel.org/stable/c/d6621f60192fe10c047a4487be42a6f4c150707f
- git.kernel.org/stable/c/ea9f65b27c8404e164848ebff1443310fd187629
- access.redhat.com/errata/RHSA-2026:22900
- access.redhat.com/errata/RHSA-2026:22940
- access.redhat.com/errata/RHSA-2026:22964
- access.redhat.com/errata/RHSA-2026:23224
- access.redhat.com/errata/RHSA-2026:23237
- access.redhat.com/errata/RHSA-2026:24343
- access.redhat.com/errata/RHSA-2026:25044
- access.redhat.com/errata/RHSA-2026:25120
- access.redhat.com/errata/RHSA-2026:25121
- access.redhat.com/errata/RHSA-2026:25181
- access.redhat.com/errata/RHSA-2026:25186
- access.redhat.com/errata/RHSA-2026:25191
Vendor advisories and official records. Exploit/PoC links are deliberately left out.