CVE-2026-43501: Linux Kernel buffer overflow (CVSS 9.8)

Description

In the Linux kernel, the following vulnerability has been resolved: ipv6: rpl: reserve mac_len headroom when recompressed SRH grows ipv6_rpl_srh_rcv() decompresses an RFC 6554 Source Routing Header, swaps the next segment into ipv6_hdr->daddr, recompresses, then pulls the old header and pushes the new one plus the IPv6 header back. The recompressed header can be larger than the received one when the swap reduces the common-prefix length the segments share with daddr (CmprI=0, CmprE>0, seg[0][0] != daddr[0] gives the maximum +8 bytes). pskb_expand_head() was gated on segments_left == 0, so on earlier segments the push consumed unchecked headroom. Once skb_push() leaves fewer than skb->mac_len bytes in front of data, skb_mac_header_rebuild()'s call to: skb_set_mac_header(skb, -skb->mac_len); will store (data - head) - mac_len into the u16 mac_header field, which wraps to ~65530, and the following memmove() writes mac_len bytes ~64KiB past skb->head. A single AF_INET6/SOCK_RAW/IPV6_HDRINCL packet over lo with a two segment type-3 SRH (CmprI=0, CmprE=15) reaches headroom 8 after one pass; KASAN reports a 14-byte OOB write in ipv6_rthdr_rcv. Fix this by expanding the head whenever the remaining room is less than the push size plus mac_len, and request that much extra so the rebuilt MAC header fits afterwards.

CVSS 3.1 breakdown

Attack vectorNetwork

Attack complexityLow

Privileges requiredNone

User interactionNone

ScopeUnchanged

ConfidentialityHigh

IntegrityHigh

AvailabilityHigh

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

Affected products

Linux Kernel≥ 5.11 < 5.15.209 · ≥ 5.16 < 6.1.175 · ≥ 5.7 < 5.10.258 · ≥ 6.13 < 6.18.27

Remediation

Fixed in

Linux Kernel≥ 5.15.209

Patch & vendor advisories

References

and 9 more references

Related CVEs

Recent high-severity vulnerabilities sharing a weakness type.

Frequently asked

Is CVE-2026-43501 being actively exploited?

CVE-2026-43501 is not in the CISA KEV catalog. Its EPSS exploit probability is 0.99%.

How severe is CVE-2026-43501?

CVE-2026-43501 has a CVSS 3.1 base score of 9.8, rated critical. EPSS estimates a 0.99% probability of exploitation.

Which products are affected by CVE-2026-43501?

Affected products include Linux Kernel.

How do I fix CVE-2026-43501?

Upgrade affected software to a fixed version, for example Linux Kernel 5.15.209 or later, then confirm no affected versions remain in your inventory.

How Secuno handles this

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