Out-of-bounds Read Affecting kernel6.12-devel package, versions <1:6.12.113-138.209.amzn2023
Threat Intelligence
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Test your applications- Snyk IDSNYK-AMZN2023-KERNEL612DEVEL-21810371
- published29 Oct 2026
- disclosed18 Oct 2026
Introduced: 18 Oct 2026
NewCVE-2026-98852 (opens in a new tab)How to fix?
Upgrade Amazon-Linux:2023 kernel6.12-devel to version 1:6.12.113-138.209.amzn2023 or higher.
This issue was patched in ALAS2023-2026-3335.
NVD Description
Note: Versions mentioned in the description apply only to the upstream kernel6.12-devel package and not the kernel6.12-devel package as distributed by Amazon-Linux.
See How to fix? for Amazon-Linux:2023 relevant fixed versions and status.
In the Linux kernel, the following vulnerability has been resolved:
net: extend IPv6 exthdr detection of tunneled packets
Commit c4336a07eb6b ("net: correctly handle tunneled traffic on IPV6_CSUM GSO fallback") split skb_gso_has_extension_hdr() into mutually exclusive branches on skb->encapsulation. This did not yet address all paths:
With skb->encapsulation set, the outer header is not checked. IPv6 tunnels such as ip6_gre and ip6_tunnel add an outer Destination Options header by default (encap_limit). Their GSO packets skip software GSO, then skb_csum_hwoffload_help() sees the outer extension header and calls skb_checksum_help() on the GSO skb, which warns and drops it.
Tunnels over IPv6 without an outer transport header, such as ip6_tunnel, leave skb->transport_header at the inner transport header. skb_network_header_len() then spans the outer IPv6, tunnel and inner IP headers, a false positive.
UDP tunnels without an inner network header, such as SCTP-in-UDP or PSP, have no inner IPv6 header to check. Decide on the outer header alone.
Directly dereferencing inner_ip_hdr(skb)->version without skb_header_pointer() is unsafe.
Instead, check ipv6_ext_hdr(nexthdr) on the outer IPv6 header and, if set, on the inner IPv6 header. Read the headers with skb_header_pointer(). Keep the skb_network_header_len() check when !skb->encapsulation to also catch encapsulated packets without skb->encapsulation (e.g., virtio).
Use the same helper in skb_csum_hwoffload_help(). Its open coded test has the false positive of (2) and ignores the inner header.
Background: checksum offload of tunneled packets invariants:
Non-GSO skb:
- If the inner packet is CHECKSUM_PARTIAL, Local Checksum Offload computes the outer checksum in software and the device offloads only the inner L4 checksum.
- If the inner packet is CHECKSUM_NONE (e.g., SCTP-in-UDP, ESP-in-UDP, Remote Checksum Offload), the device offloads the outer UDP or GRE checksum instead.
GSO skb:
- A device with NETIF_F_GSO_UDP_TUNNEL_CSUM or NETIF_F_GSO_GRE_CSUM computes both inner and outer checksums per segment. The outer checksum is seeded with only the pseudo-header checksum.
A NETIF_F_IPV6_CSUM device must parse through the outer headers to reach the inner ones.
References
- http://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2026-98852
- https://git.kernel.org/stable/c/44ba9dc568c878b699d05e7cf699572dc9df4b59
- https://git.kernel.org/stable/c/5f0764cb1c81a9712bce605d38efe6d844a70b29
- https://git.kernel.org/stable/c/aa480f05aed7a9eee87d4a6fc90647fe9679c670
- https://git.kernel.org/stable/c/cabacdf98e09eb74599c4d97d7bd7fd659598fb7
- https://git.kernel.org/stable/c/fdbd83c2d929ec968b37d2f75149a79440e328ff