Bug 2516530 (CVE-2026-72408)

Summary: CVE-2026-72408 kernel: geneve: gate GRO hint in geneve_gro_complete() on gs->gro_hint
Product: [Other] Security Response Reporter: OSIDB Bzimport <bzimport>
Component: vulnerabilityAssignee: Product Security DevOps Team <prodsec-dev>
Status: NEW --- QA Contact:
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Priority: medium    
Version: unspecifiedCC: rhel-process-autobot, watson-tool-maintainers
Target Milestone: ---Keywords: Security
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Hardware: All   
OS: Linux   
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A flaw was found in the Linux kernel's geneve component. An attacker can send a specially crafted Geneve (Generic Network Virtualization Encapsulation) packet that exploits a discrepancy in how GRO (Generic Receive Offload) hints are processed. The geneve_gro_complete() function processes these hints unconditionally, even when the geneve_gro_receive() function does not validate them. This allows an attacker to trigger an out-of-bounds read, which can lead to a system crash and a denial of service.
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Description OSIDB Bzimport 2026-08-15 06:17:20 UTC 
In the Linux kernel, the following vulnerability has been resolved:

geneve: gate GRO hint in geneve_gro_complete() on gs->gro_hint

geneve_gro_receive() reads the GRO hint through geneve_sk_gro_hint_off(),
which honours it only when the socket enabled IFLA_GENEVE_GRO_HINT
(gs->gro_hint). geneve_gro_complete() instead calls the low-level
geneve_opt_gro_hint_off() and acts on the hint unconditionally.

On a tunnel without the hint, receive aggregates the frames as plain
ETH_P_TEB while complete still honours an attacker-supplied hint option: it
inflates gh_len by gro_hint->nested_hdr_len (u8) and redirects the dispatch
type, so the inner gro_complete handler runs at nhoff + gh_len, an offset
receive never pulled nor validated, reading out of bounds of the skb head:

  BUG: KASAN: slab-out-of-bounds in ipv6_gro_complete (net/ipv6/ip6_offload.c:196)
  Read of size 1 at addr ffff88800fe91980 by task exploit/153
   ipv6_gro_complete (net/ipv6/ip6_offload.c:196)
   geneve_gro_complete (drivers/net/geneve.c:965)
   udp_gro_complete (net/ipv4/udp_offload.c:940)
   inet_gro_complete (net/ipv4/af_inet.c:1621)
   __gro_flush (net/core/gro.c:306)

Gate the complete path on gs->gro_hint too via geneve_sk_gro_hint_off(), so
both paths agree. Tunnels that enable the hint are unaffected.
Comment 1 Keith Grant 2026-08-19 15:43:21 UTC 
Upstream advisory:
https://lore.kernel.org/linux-cve-announce/2026081523-CVE-2026-72408-bbc1@gregkh/T