Bug 2521409 (CVE-2026-74597)

Summary: CVE-2026-74597 kernel: ip6_tunnel: clear skb2->cb[] in ip6ip6_err()
Product: [Other] Security Response Reporter: OSIDB Bzimport <bzimport>
Component: vulnerabilityAssignee: Product Security DevOps Team <prodsec-dev>
Status: NEW --- QA Contact:
Severity: high Docs Contact:
Priority: high    
Version: unspecifiedCC: rhel-process-autobot, watson-tool-maintainers
Target Milestone: ---Keywords: Security
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Hardware: All   
OS: Linux   
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Doc Text:
A flaw was found in the Linux kernel's IPv6 (Internet Protocol version 6) tunnel error handling. A remote attacker could send a specially crafted IPv6 ICMP (Internet Control Message Protocol) error packet with a malformed inner destination-options header. This could lead to memory corruption within the kernel's socket buffer shared information, potentially causing a denial of service (DoS) on the system.
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oVirt Team: --- RHEL 7.3 requirements from Atomic Host:
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Description OSIDB Bzimport 2026-08-22 15:44:11 UTC 
In the Linux kernel, the following vulnerability has been resolved:

ip6_tunnel: clear skb2->cb[] in ip6ip6_err()

ip6ip6_err() clones an outer IPv6 ICMP error skb, pulls it to the
quoted inner IPv6 packet, and then passes the clone to icmpv6_send().
The clone still carries the outer packet's inet6_skb_parm in skb->cb.

If the outer packet had a Home Address Option, IP6CB(skb2)->dsthao
remains non-zero after skb_pull(). icmpv6_send() later calls
mip6_addr_swap(), which uses that stale dsthao offset against the quoted
inner packet. A malformed inner destination-options header can then make
the HAO lookup and address swap run past the end of the quoted packet
and corrupt skb_shared_info.

Clear skb2->cb[] before pulling the quoted inner IPv6 packet so the
reply path does not reuse metadata left by the outer IPv6 stack.
Comment 1 Mauro Matteo Cascella 2026-08-24 12:06:43 UTC 
Upstream advisory:
https://lore.kernel.org/linux-cve-announce/2026082214-CVE-2026-74597-98fc@gregkh/T