UBUNTU-CVE-2026-93805: Medium severity ubuntu/linux vulnerability
In the Linux kernel, the following vulnerability has been resolved: wifi: cfg80211: validate rx/tx MLME callback frame lengths before access cfg80211rxmlmemgmt() and cfg80211txmlmemgmt() call tracepoints before rejecting frames shorter than the frame-control field. After that, they only require len >= 2 before dispatching into subtype handlers that assume their fixed fields are present. The frames that trip this are not shorter than 2 bytes; they are short relative to their subtype. mwifiex is a concrete in-tree example on the length side: mwifiexprocessmgmtpacket() only requires a 4-address ieee80211hdr plus the 2-byte firmware length prefix before handing the frame to cfg80211rxmlmemgmt(). After stripping the length prefix and removing addr4, pktlen can be exactly 24: a bare 3-address management header with no reason-code body. The existing WARNON(len < 2) does not fire on such a frame, and cfg80211processdeauth() then reads u.deauth.reasoncode as a two-byte access starting at offset 24, immediately past the 24-byte buffer. Add a frame-control length gate, then validate each subtype's minimum frame size in an if/else-if chain that mirrors the dispatch logic. Trace only after the frame is known to be well-formed. Side effects of this change: - The WARNON(len < 2) is dropped. It only guarded the framecontrol read, never the subtype fixed fields, and it does not fire on the frames that actually trigger the out-of-bounds read (which are >= 2). The len >= 2 check is kept as the guard before dereferencing framecontrol, but without the warning: these are exported callbacks and a malformed frame from a driver should be dropped silently rather than backtraced. - cfg80211txmlmemgmt() previously routed every non-deauth subtype through disassociation handling; it now silently ignores unrecognised subtypes.
Affected Software
Remediation
Recommended actions to resolve this vulnerability, in priority order.
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ubuntu/linux-aws-5.15to a version that resolves this vulnerability.Fixed in 5.15.0-1119.126~20.04.1 - Upgrade
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ubuntu/linux-riscvto a version that resolves this vulnerability.Fixed in 7.0.0-42.42.1 - Compensating control
In cfg80211_rx_mlme_mgmt() and cfg80211_tx_mlme_mgmt(), require len >= 2 before reading frame_control, add a frame-control length gate, and validate each management subtype's minimum frame size in an if/else-if chain matching dispatch logic. Treat a 24-byte 3-address management header with no reason-code body as too short for deauthentication/disassociation handlers, require the subtype-specific fixed fields before dispatch, silently drop malformed frames, and emit tracepoints only after the frame is validated.