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CVE-2026-64037
wifi: iwlwifi: mld: fix TSO segmentation explosion when AMSDU is disabled
Published 2026-07-19 (3 months ago) by the Linux kernel CNA. Subsystem drivers/net. Debian urgency: unimportant.
What to do, per Debian release
Debian's own status for CVE-2026-64037 in every release this site tracks, and what each one means in practice. Every status below is the one the Debian Security Team publishes for this CVE. source
| Release | Status | Version | What this means |
|---|---|---|---|
| Debian 12bookworm | not affected | 6.1.190-1 | Nothing to do. bookworm never shipped the vulnerable code. |
| Debian 13trixie | not affected | 6.12.113-1 | Nothing to do. trixie never shipped the vulnerable code. |
| Debian 14forky | fixed | 7.0.12-1 | Update the kernel and reboot. Fixed in 7.0.12-1. A running kernel keeps the old code until the machine restarts. |
| Debian unstablesid | fixed | 7.0.12-1 | Update the kernel and reboot. Fixed in 7.0.12-1. A running kernel keeps the old code until the machine restarts. |
The vulnerability
What the bug is
When the TLC notification disables AMSDU for a TID, the MLD driver sets max_tid_amsdu_len to the sentinel value 1. The TSO segmentation path in iwl_mld_tx_tso_segment() checks for zero but not for this sentinel, allowing it to reach the num_subframes calculation: num_subframes = (max_tid_amsdu_len + pad) / (subf_len + pad) = (1 + 2) / (1534 + 2) = 0 This zero propagates to iwl_tx_tso_segment() which sets: gso_size = num_subframes * mss = 0 Calling skb_gso_segment() with gso_size=0 creates over 32000 tiny segments from a single GSO skb. This floods the TX ring with ~1024 micro-frames (the rest are purged), creating a massive burst of TX completion events that can lead to memory corruption and a subsequent use-after-free in TCP's retransmit queue (refcount underflow in tcp_shifted_skb, NULL deref in tcp_rack_detect_loss). The MVM driver is immune because it checks mvmsta->amsdu_enabled before reaching the num_subframes calculation. The MLD driver has no equivalent bitmap check and relies solely on max_tid_amsdu_len, which does not catch the sentinel value. Fix this by detecting the sentinel value (max_tid_amsdu_len == 1) at the existing check and falling back to non-AMSDU TSO segmentation. Also add a WARN_ON_ONCE guard after the num_subframes division as defense-in-depth to catch any future code paths that produce zero through a different mechanism.
Where it lives
The fix touches these files. If the subsystem is one you do not use, the practical exposure is lower, though the package is still the vulnerable one.
drivers/net/wireless/intel/iwlwifi/mld/tx.c
- What this is
- INTEL WIRELESS WIFI LINK (iwlwifi)MAINTAINERS section matched on drivers/net/wireless/intel/iwlwifi/ · linux-wireless@vger.kernel.org · Supported
Check it on the machine
grep -wE 'CONFIG_IWLMEI|CONFIG_IWLMLD|CONFIG_IWLWIFI|CONFIG_WLAN|CONFIG_WLAN_VENDOR_INTEL' /boot/config-$(uname -r)Reads the booted kernel's own configuration, on the machine and nowhere else. =y is built in, =m is a module, and an is not set line means the code is not there.
Show whether Debian builds this, per release
Debian does not build this code in 2 releases. The build rule could not be established for 2 releases, so nothing is claimed about those.
- bookworm, trixie?
- forky, sidn
- ?
- not established - no Makefile entry for the affected file
- n
- not enabled on any flavour - this release does not build the code
Where a release above reads "not established", no build rule for the affected file was found in that release's kernel tree. That is a gap in this lookup, not a finding that the code is absent.
- Build switches
- CONFIG_IWLMEI, CONFIG_IWLMLD, CONFIG_IWLWIFI, CONFIG_WLAN, CONFIG_WLAN_VENDOR_INTEL
- Reads as
- all on means the file is compiled; any one off means it is not.
From the configuration Debian publishes for every kernel flavour it builds. It covers only the architectures Debian ships a linux-config package for, and nothing about a kernel you built yourself. Debian's own status above stays authoritative about the source package.MAINTAINERS kbuild Makefiles Debian linux-config packages
Signals
- Published
- 2026-07-19 (3 months ago)source
- CVSS
- 9.8 critical
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:Hsource recompute it - Attack vector
- network (AV:N)source
- EPSS
- 0.43%, higher than 35.8% of all CVEssource
- CISA KEV
- not listedthe KEV catalogue
- Debian urgency
- unimportantsource
- Subsystem
- drivers/net
Upstream fixes
The versions the CNA records as introducing and fixing this, and the commit for each. source
| Introduced | Fixed in | Commit |
|---|---|---|
| 6.15 | 6.18.34 | 9e360e610a73 |
| 6.15 | 7.0.11 | cbe1c8245e44 |
| 6.15 | 7.1 | 92cee08dc4f0 |
Why the CNA scored it this way
Quoted from the kernel CNA's own scoring file, word for word. A highlighted metric carries the most severe value CVSS v3.1 defines for it, which is what pushes the score up. source
- AV:NAttack vector, network
- A remote peer can trigger the vulnerable iwlwifi MLD TX/TSO path by inducing large outbound TCP traffic (responses, uploads, or sustained transfers) on a WiFi 7 Intel system; no adjacent WiFi frame injection or local syscall access is required to reach the bug.
- AC:LAttack complexity, low
- An attacker controls the timing and volume of TCP traffic that produces GSO skbs, and TLC AMSDU-disable notifications are normal firmware rate-adaptation behavior that occurs during routine WiFi use; repeated attempts can reliably hit the sentinel state without conditions outside attacker influence.
- PR:NPrivileges required, none
- Exploitation requires only the ability to generate or solicit network traffic on the victim's WiFi interface; no local account, CAP_NET_ADMIN, or root privileges are needed on the victim host.
- UI:NUser interaction, none
- No victim user action beyond normal automated network activity is required; a remote attacker can trigger the condition with crafted or high-volume TCP sessions alone.
- S:UScope, unchanged
- The resulting memory corruption and TCP retransmit-queue UAF occur within kernel/network-driver scope and do not cross a VM, container, or IOMMU security boundary.
- C:HConfidentiality impact, high
- The fix commit documents memory corruption and a subsequent use-after-free in TCP's retransmit queue (refcount underflow in tcp_shifted_skb), which per kernel guidance enables arbitrary kernel memory read primitives.
- I:HIntegrity impact, high
- The same UAF and refcount corruption in the TCP retransmit path can be leveraged for arbitrary kernel writes and potential control-flow hijacking, not merely a bounded data change.
- A:HAvailability impact, high
- The segmentation explosion floods the TX ring with ~1024 micro-frames and a burst of completion events, causing kernel instability including NULL dereference in tcp_rack_detect_loss and system crash/hang.