CVE-2026-23276
Undergoing Analysis Undergoing Analysis - In Progress
Stack Overflow in Linux Kernel Tunnel Transmit Functions

Publication date: 2026-03-20

Last updated on: 2026-05-22

Assigner: kernel.org

Description
In the Linux kernel, the following vulnerability has been resolved: net: add xmit recursion limit to tunnel xmit functions Tunnel xmit functions (iptunnel_xmit, ip6tunnel_xmit) lack their own recursion limit. When a bond device in broadcast mode has GRE tap interfaces as slaves, and those GRE tunnels route back through the bond, multicast/broadcast traffic triggers infinite recursion between bond_xmit_broadcast() and ip_tunnel_xmit()/ip6_tnl_xmit(), causing kernel stack overflow. The existing XMIT_RECURSION_LIMIT (8) in the no-qdisc path is not sufficient because tunnel recursion involves route lookups and full IP output, consuming much more stack per level. Use a lower limit of 4 (IP_TUNNEL_RECURSION_LIMIT) to prevent overflow. Add recursion detection using dev_xmit_recursion helpers directly in iptunnel_xmit() and ip6tunnel_xmit() to cover all IPv4/IPv6 tunnel paths including UDP encapsulated tunnels (VXLAN, Geneve, etc.). Move dev_xmit_recursion helpers from net/core/dev.h to public header include/linux/netdevice.h so they can be used by tunnel code. BUG: KASAN: stack-out-of-bounds in blake2s.constprop.0+0xe7/0x160 Write of size 32 at addr ffff88810033fed0 by task kworker/0:1/11 Workqueue: mld mld_ifc_work Call Trace: <TASK> __build_flow_key.constprop.0 (net/ipv4/route.c:515) ip_rt_update_pmtu (net/ipv4/route.c:1073) iptunnel_xmit (net/ipv4/ip_tunnel_core.c:84) ip_tunnel_xmit (net/ipv4/ip_tunnel.c:847) gre_tap_xmit (net/ipv4/ip_gre.c:779) dev_hard_start_xmit (net/core/dev.c:3887) sch_direct_xmit (net/sched/sch_generic.c:347) __dev_queue_xmit (net/core/dev.c:4802) bond_dev_queue_xmit (drivers/net/bonding/bond_main.c:312) bond_xmit_broadcast (drivers/net/bonding/bond_main.c:5279) bond_start_xmit (drivers/net/bonding/bond_main.c:5530) dev_hard_start_xmit (net/core/dev.c:3887) __dev_queue_xmit (net/core/dev.c:4841) ip_finish_output2 (net/ipv4/ip_output.c:237) ip_output (net/ipv4/ip_output.c:438) iptunnel_xmit (net/ipv4/ip_tunnel_core.c:86) gre_tap_xmit (net/ipv4/ip_gre.c:779) dev_hard_start_xmit (net/core/dev.c:3887) sch_direct_xmit (net/sched/sch_generic.c:347) __dev_queue_xmit (net/core/dev.c:4802) bond_dev_queue_xmit (drivers/net/bonding/bond_main.c:312) bond_xmit_broadcast (drivers/net/bonding/bond_main.c:5279) bond_start_xmit (drivers/net/bonding/bond_main.c:5530) dev_hard_start_xmit (net/core/dev.c:3887) __dev_queue_xmit (net/core/dev.c:4841) ip_finish_output2 (net/ipv4/ip_output.c:237) ip_output (net/ipv4/ip_output.c:438) iptunnel_xmit (net/ipv4/ip_tunnel_core.c:86) ip_tunnel_xmit (net/ipv4/ip_tunnel.c:847) gre_tap_xmit (net/ipv4/ip_gre.c:779) dev_hard_start_xmit (net/core/dev.c:3887) sch_direct_xmit (net/sched/sch_generic.c:347) __dev_queue_xmit (net/core/dev.c:4802) bond_dev_queue_xmit (drivers/net/bonding/bond_main.c:312) bond_xmit_broadcast (drivers/net/bonding/bond_main.c:5279) bond_start_xmit (drivers/net/bonding/bond_main.c:5530) dev_hard_start_xmit (net/core/dev.c:3887) __dev_queue_xmit (net/core/dev.c:4841) mld_sendpack mld_ifc_work process_one_work worker_thread </TASK>
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Meta Information
Published
2026-03-20
Last Modified
2026-05-22
Generated
2026-06-16
AI Q&A
2026-03-20
EPSS Evaluated
2026-06-15
NVD
CVE-2026-23276
EUVD
EUVD-2026-13612
Affected Vendors & Products
Showing 7 associated CPEs
Vendor Product Version / Range
linux linux_kernel 7.0
linux linux_kernel 7.0
linux linux_kernel 7.0
linux linux_kernel From 6.13 (inc) to 6.18.19 (exc)
linux linux_kernel From 6.19 (inc) to 6.19.9 (exc)
linux linux_kernel From 2.6.35.9 (inc) to 2.6.36 (exc)
linux linux_kernel From 2.6.37 (inc) to 6.12.78 (exc)
Helpful Resources
Exploitability
CWE
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KEV
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CWE ID Description
CWE-674 The product does not properly control the amount of recursion that takes place, consuming excessive resources, such as allocated memory or the program stack.
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Executive Summary

This vulnerability exists in the Linux kernel's network tunnel transmit (xmit) functions, specifically iptunnel_xmit and ip6tunnel_xmit, which lacked their own recursion limit.

When a bond device in broadcast mode has GRE tap interfaces as slaves, and those GRE tunnels route traffic back through the bond, multicast or broadcast traffic can cause infinite recursion between bond_xmit_broadcast() and ip_tunnel_xmit()/ip6_tnl_xmit().

This infinite recursion leads to a kernel stack overflow, which can cause system instability or crashes.

The existing recursion limit (XMIT_RECURSION_LIMIT) was insufficient because tunnel recursion involves more stack usage per level, so a lower limit (IP_TUNNEL_RECURSION_LIMIT) was introduced to prevent overflow.

Additionally, recursion detection helpers were added directly in the tunnel transmit functions to cover all IPv4/IPv6 tunnel paths, including UDP encapsulated tunnels like VXLAN and Geneve.

Impact Analysis

This vulnerability can cause a kernel stack overflow due to infinite recursion in network tunnel transmit functions when certain network configurations are used.

The impact includes potential system crashes, instability, or denial of service as the kernel stack overflows and the system may become unresponsive or reboot.

Systems using bonded network devices with GRE tap interfaces in broadcast mode are particularly at risk if multicast or broadcast traffic triggers this recursion.

Compliance Impact

I don't know

Detection Guidance

I don't know

Mitigation Strategies

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