CVE-2026-53182: Linux Kernel Buffer Overflow Vulnerability

CVE-2026-53182 Overview

CVE-2026-53182 is a Linux kernel vulnerability in the wifi/nl80211 subsystem. The function nl80211_parse_rnr_elems() stores the parsed element count in a u8-backed cfg80211_rnr_elems::cnt field and uses that count to size a flexible array allocation. Without a proper bound check, nested NL80211_ATTR_EMA_RNR_ELEMS input can exceed the 255-element capacity of the counter, leading to an inconsistency between the parser and the data structure it fills. The fix rejects oversized Enhanced Multi-BSSID Advertisement (EMA) Reduced Neighbor Report (RNR) lists once the count reaches 255, matching the existing bound check in nl80211_parse_mbssid_elems().

Critical Impact
A local user with the capability to issue nl80211 netlink commands can submit oversized EMA RNR element lists, triggering parser/allocation inconsistencies in the wireless configuration code path.

Affected Products

Linux kernel wifi/nl80211 subsystem (mainline and stable branches prior to the fix)
Distributions shipping affected stable kernel versions referenced by the upstream stable commits
Systems exposing wireless configuration interfaces through cfg80211/nl80211

Discovery Timeline

2026-06-25 - CVE-2026-53182 published to NVD
2026-06-25 - Last updated in NVD database

Technical Details for CVE-2026-53182

Vulnerability Analysis

The defect resides in nl80211_parse_rnr_elems(), which parses nested NL80211_ATTR_EMA_RNR_ELEMS netlink attributes used to convey EMA RNR information elements for multi-BSSID wireless beacons. The parser tracks the number of parsed elements using a u8 counter inside cfg80211_rnr_elems::cnt. That same counter is used to size the flexible array member holding the parsed elements.

Because the parser did not stop accepting input when the counter reached its u8 maximum of 255, the increment could wrap or produce an element count inconsistent with the array allocation. This breaks an invariant between the parser and the destination data structure, which can lead to memory safety issues during subsequent processing of the parsed RNR list.

Root Cause

The root cause is missing input validation on the number of nested EMA RNR elements before incrementing the u8 counter. The sibling function nl80211_parse_mbssid_elems() already enforces this bound, but nl80211_parse_rnr_elems() did not. This is an input validation flaw [CWE-1284-class] tied directly to the integer width of the destination counter.

Attack Vector

The attack surface is local, through the netlink-based nl80211 interface used to configure wireless devices. A process able to send nl80211 commands (typically requiring CAP_NET_ADMIN) can craft a netlink message containing more than 255 nested NL80211_ATTR_EMA_RNR_ELEMS entries. The malformed message exercises the unchecked parser path before the upstream patch rejects it.

No verified public proof-of-concept is referenced for this CVE. The remediation is delivered as upstream kernel commits; see Kernel Git Commit 265c07c0 and Kernel Git Commit fc0ec2fc for the canonical fix.

Detection Methods for CVE-2026-53182

Indicators of Compromise

Unexpected kernel warnings, oops messages, or memory corruption signatures originating from cfg80211 or nl80211 code paths in dmesg and /var/log/kern.log.
Unprivileged or unexpected processes issuing NL80211_CMD_* netlink operations that include NL80211_ATTR_EMA_RNR_ELEMS attributes.
Anomalous crashes or restarts of hostapd, wpa_supplicant, or other wireless management daemons on access-point class systems.

Detection Strategies

Audit kernel versions across the fleet and compare against the fixed stable commits to enumerate systems still exposed.
Enable kernel hardening telemetry such as KASAN or kernel lockdown on test systems to surface memory inconsistencies triggered by malformed nl80211 input.
Monitor netlink activity using auditd rules on the socket and sendmsg syscalls scoped to AF_NETLINK/NETLINK_GENERIC traffic.

Monitoring Recommendations

Forward kernel logs to a centralized logging or SIEM platform and alert on nl80211, cfg80211_rnr, or BUG:/WARNING: signatures.
Track package and kernel update state across Linux endpoints, especially access points, embedded gateways, and wireless-enabled servers.
Baseline which user-space processes legitimately issue nl80211 commands and alert on deviations.

How to Mitigate CVE-2026-53182

Immediate Actions Required

Update affected Linux systems to a kernel version that includes the upstream fix referenced by the stable commits listed in the NVD entry.
Restrict CAP_NET_ADMIN to trusted administrative accounts and service principals only, since the netlink interface requires it for wireless configuration.
On systems that do not use wireless networking, ensure cfg80211 and mac80211 modules are not loaded or are blacklisted.

Patch Information

The fix adds an explicit bound check that rejects nested NL80211_ATTR_EMA_RNR_ELEMS input once the parsed count reaches 255, before incrementing the u8 counter again. This aligns nl80211_parse_rnr_elems() with the existing bound check used by nl80211_parse_mbssid_elems(). The patches are available in the following upstream commits: 265c07c0, 30c3fa80, 4cd92957, 688fcac7, ecbf3c45, and fc0ec2fc.

Workarounds

Blacklist the cfg80211 and mac80211 kernel modules on systems that do not require wireless functionality to remove the vulnerable code path from the loaded kernel.
Limit which accounts can hold CAP_NET_ADMIN and avoid granting it to general-purpose service accounts that do not manage wireless devices.
Constrain wireless management daemons such as hostapd and wpa_supplicant with systemd hardening directives or namespaces to reduce exposure if a compromise occurs.

bash

# Verify current kernel version against fixed stable commits
uname -r

# Blacklist cfg80211/mac80211 on systems without wireless requirements
echo 'blacklist cfg80211' | sudo tee /etc/modprobe.d/disable-wireless.conf
echo 'blacklist mac80211' | sudo tee -a /etc/modprobe.d/disable-wireless.conf
sudo update-initramfs -u

# Audit processes holding CAP_NET_ADMIN
sudo getcap -r / 2>/dev/null | grep cap_net_admin