CVE-2026-80725
Received Received - Intake

Improper BIG TCP Aggregation Validation in Linux Kernel

Publication date: 2026-08-29

Last updated on: 2026-08-29

Assigner: kernel.org

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.

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Meta Information

Published
2026-08-29
Last Modified
2026-08-29
Generated
2026-08-29
AI Q&A
2026-08-29
EPSS Evaluated
N/A
NVD
CVE-2026-80725
EUVD
EUVD-2026-68066

Affected Vendors & Products

Showing 1 associated CPE
Vendor Product Version / Range
linux linux_kernel to 7.0 (exc)

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Exploitability

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CWE ID Description
CWE-UNKNOWN

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Executive Summary

This vulnerability in the Linux kernel involves improper validation of BIG TCP aggregation criteria in the Generic Receive Offload (GRO) subsystem. It allows crafted frames to bypass size checks, leading to potential out-of-bounds memory writes when processing IPv6 packets with jumbo headers. The issue arises from incorrect checks in skb_gro_receive() that permit non-compliant packets to aggregate beyond 64KB, risking system instability or crashes.

Detection Guidance

This vulnerability involves improper validation in Linux kernel's GRO (Generic Receive Offload) for BIG TCP packets. Detection requires checking kernel logs for GRO-related errors or crashes, particularly during high-traffic network conditions. Monitor for out-of-bounds writes or memmove errors in kernel logs. Use commands like dmesg | grep -i gro or journalctl -k | grep -i gro to inspect GRO-related messages.

Impact Analysis

If exploited, this vulnerability could allow an attacker to trigger memory corruption in the Linux kernel by sending specially crafted network packets. This may lead to denial-of-service conditions, system crashes, or potential privilege escalation. Systems using vulnerable kernel versions (older stable branches like 6.18.y) are at risk if BIG TCP is enabled.

Compliance Impact

This vulnerability primarily affects network packet processing in the Linux kernel, leading to potential out-of-bounds memory writes and packet corruption. It does not directly impact compliance with standards like GDPR or HIPAA, which focus on data protection and privacy. However, if exploited, it could lead to data integrity issues or unauthorized access, indirectly affecting compliance.

Mitigation Strategies

Immediately update the Linux kernel to a patched version that includes the fix for CVE-2026-80725. If updating is not immediately possible, disable GRO for BIG TCP by setting net.core.gro_normal_batch to 0 or disable GRO entirely via ethtool -K <interface> gro off. Monitor network traffic for anomalies post-mitigation.

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