Description
In the Linux kernel, the following vulnerability has been resolved:

net: gro: properly validate BIG TCP aggregation criteria

When GRO attempts to aggregate packets beyond GRO_LEGACY_MAX_SIZE (64KB),
BIG TCP should only be permitted for plain IPv4 TCP and plain IPv6 TCP
(with sufficient MAC header room to insert the temporary HBH jumbo header).

However, commit b1a78b9b9886 ("net: add support for ipv4 big tcp")
loosened the check in skb_gro_receive(), leading to several issues:

1. skb_gro_receive() checked skb_headroom(p) instead of the actual space
before the MAC header (p->mac_header). Because skb_headroom(p) includes
mac_len, crafted frames (e.g. injected via AF_PACKET) can pass the check
with p->mac_header < 8 bytes. When ipv6_gro_complete() inserts the
temporary HBH jumbo header, the memmove() starts before skb->head,
causing an out-of-bounds write and wrapping skb->mac_header.
2. It allowed non-IP protocols such as software VLAN (ETH_P_8021Q /
ETH_P_8021AD) to aggregate beyond 64KB because
p->protocol != ETH_P_IPV6 was true.
3. It checked p->encapsulation instead of NAPI_GRO_CB(skb)->encap_mark,
allowing encapsulated flows (e.g. SIT / IPv6-in-IPv4) to aggregate
beyond 64KB.

Fix skb_gro_receive() to strictly enforce:
- NAPI_GRO_CB(skb)->proto == IPPROTO_TCP
- Not encapsulated (!NAPI_GRO_CB(skb)->encap_mark && !p->encapsulation)
- Protocol must be either ETH_P_IP or ETH_P_IPV6
- If ETH_P_IPV6, p->mac_header must be at least
sizeof(struct hop_jumbo_hdr)

Returning -E2BIG from skb_gro_receive() ensures that packets which cannot
become BIG TCP are cleanly flushed at <= 64KB and delivered intact without
dropping.

This issue does not exist in mainline (7.0+) because the subsystem was
rewritten in commit 81be30c1f5f2 ("net/ipv6: Drop HBH for BIG TCP on RX
side"), making this fix relevant only for older stable branches like
6.18.y.
Published: 2026-08-29
Score: n/a
EPSS: n/a
KEV: No
Impact: n/a
Action: n/a
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History

Sat, 29 Aug 2026 07:00:00 +0000

Type Values Removed Values Added
Description In the Linux kernel, the following vulnerability has been resolved: net: gro: properly validate BIG TCP aggregation criteria When GRO attempts to aggregate packets beyond GRO_LEGACY_MAX_SIZE (64KB), BIG TCP should only be permitted for plain IPv4 TCP and plain IPv6 TCP (with sufficient MAC header room to insert the temporary HBH jumbo header). However, commit b1a78b9b9886 ("net: add support for ipv4 big tcp") loosened the check in skb_gro_receive(), leading to several issues: 1. skb_gro_receive() checked skb_headroom(p) instead of the actual space before the MAC header (p->mac_header). Because skb_headroom(p) includes mac_len, crafted frames (e.g. injected via AF_PACKET) can pass the check with p->mac_header < 8 bytes. When ipv6_gro_complete() inserts the temporary HBH jumbo header, the memmove() starts before skb->head, causing an out-of-bounds write and wrapping skb->mac_header. 2. It allowed non-IP protocols such as software VLAN (ETH_P_8021Q / ETH_P_8021AD) to aggregate beyond 64KB because p->protocol != ETH_P_IPV6 was true. 3. It checked p->encapsulation instead of NAPI_GRO_CB(skb)->encap_mark, allowing encapsulated flows (e.g. SIT / IPv6-in-IPv4) to aggregate beyond 64KB. Fix skb_gro_receive() to strictly enforce: - NAPI_GRO_CB(skb)->proto == IPPROTO_TCP - Not encapsulated (!NAPI_GRO_CB(skb)->encap_mark && !p->encapsulation) - Protocol must be either ETH_P_IP or ETH_P_IPV6 - If ETH_P_IPV6, p->mac_header must be at least sizeof(struct hop_jumbo_hdr) Returning -E2BIG from skb_gro_receive() ensures that packets which cannot become BIG TCP are cleanly flushed at <= 64KB and delivered intact without dropping. This issue does not exist in mainline (7.0+) because the subsystem was rewritten in commit 81be30c1f5f2 ("net/ipv6: Drop HBH for BIG TCP on RX side"), making this fix relevant only for older stable branches like 6.18.y.
Title net: gro: properly validate BIG TCP aggregation criteria
First Time appeared Linux
Linux linux Kernel
CPEs cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*
Vendors & Products Linux
Linux linux Kernel
References

Subscriptions

Linux Linux Kernel
cve-icon MITRE

Status: PUBLISHED

Assigner: Linux

Published:

Updated: 2026-08-29T06:40:30.300Z

Reserved: 2026-08-26T14:34:25.789Z

Link: CVE-2026-80725

cve-icon Vulnrichment

No data.

cve-icon NVD

Status : Received

Published: 2026-08-29T07:16:54.573

Modified: 2026-08-29T07:16:54.573

Link: CVE-2026-80725

cve-icon Redhat

No data.

cve-icon OpenCVE Enrichment

Updated: 2026-08-29T08:30:06Z

Weaknesses

No weakness.