Missing multi-link parsing validation in wpa_supplicant and hostapd

Published: June 5, 2026
Latest version available from: https://w1.fi/security/2026-1/

Vulnerability

Vulnerabilities in parsing and use of received multi-link (MLO/EHT/IEEE
802.11be/Wi-Fi 7) information has been identified in hostapd and
wpa_supplicant. These issues show up in various cases where frames
including information on affiliated links are parsed and processed in
both AP and STA modes. The issues can result in process termination due
to buffer read overflow checks and memory corruption.

The issues for AP mode (hostapd or wpa_supplicant) can result in
denial-of-service attacks due to process termination and small memory
corruption that could theoretically cause other issues, but it does not
seem likely that those could be exploiting in practice. Affected areas
can be reached by sending invalid Management frames without needing
authentication or user action on the target device.

The issues in STA mode (wpa_supplicant) can result in denial-of-service
attacks due to process termination and memory corruption. Affected areas
can be reached by sending invalid Management frames without needing
authentication or user action on the target device.


Vulnerable versions/configurations

hostapd v2.11 and newer snapshots from the repository before v2.12 with
CONFIG_IEEE80211BE build option enabled.

wpa_supplicant v2.11 and newer snapshots from the repository before
v2.12.


Acknowledgments

Thanks to discovering and reporting the issues to:

- Missing link ID validation check in AP mode association processing:
  Sebastián Alba Vives (@Sebasteuo / 0xS4bb1) and independent discovery
  and report by Abhinav Agarwal
- Missing link ID validation check in wpa_supplicant scan result
  processing: (TBC)
- Incorrect validation of MLE common info length:
  Martin Brodeur, at Fluentlogic

In addition to the reported issues, code review of similar areas showed
other potential areas that did not have complete validation of the
received messages. Most of these did not seem to result into opening
potential additional attacks, but more thorough validation has been
added to minimize risk for unknown issues or issues enabled by future
extensions of the functionality in this area.


Possible mitigation steps

- Update to hostapd v2.12 or newer once available

- Merge the following commits to an earlier hostapd and wpa_supplicant
  version and rebuild:

https://git.w1.fi/cgit/hostap/commit/?id=46dd5a4ffc9bcf44cf8fc45120b3e1e5ec922187
AP MLD: Fix link ID validation in Basic MLE parsing

https://git.w1.fi/cgit/hostap/commit/?id=aa9d345887389a251c63a3781d2ad2940d079193
BSS: Add bounds check for link_id in Basic MLE parsing

https://git.w1.fi/cgit/hostap/commit/?id=a8531e3d871e6fa72f2f85d91e9f787326b2af8b
MLD: Validate MLE Link ID fields in association rejection case

https://git.w1.fi/cgit/hostap/commit/?id=56216d113909650ae59621dc2dd16157afb94948
Verify MLD link ID validity in get_basic_mle_link_id()

https://git.w1.fi/cgit/hostap/commit/?id=e4bd3442c2223802bf8c4a4d868e3b9443c7caf4
MLD: Verify link ID validity in MLE in reconfiguration

https://git.w1.fi/cgit/hostap/commit/?id=ce1a8612e309fe86133ecf05ffb452b0bdf3b035
AP MLD: Verify AP MLD link ID validity before updating bitmap of links

https://git.w1.fi/cgit/hostap/commit/?id=41c86a2ebed50567c73de23c102c2bf83eb883f2
MLD: Fix length check in common info for association failure cases

https://git.w1.fi/cgit/hostap/commit/?id=595194d0305189922a057e8ea8b743a1bd8d2d29
BSS: Fix validate of ML common info length during scan result parsing

- The relevant commits rebased on to of v2.11 releases are available
  from https://w1.fi/security/2026-1/