CVE-2026-74586 in Linux
Summary
by MITRE • 08/22/2026
In the Linux kernel, the following vulnerability has been resolved:
sctp: clear new_transport when removing a peer
sctp_process_asconf_param() stores a newly added peer transport in asoc->new_transport. After all parameters in the ASCONF chunk have been processed, sctp_sf_do_asconf() uses this pointer to send a HEARTBEAT to the new transport.
An authenticated ASCONF from a remote SCTP peer can add a transport and remove it again with a wildcard DEL-IP parameter in the same chunk. The wildcard deletion preserves the transport on which the ASCONF arrived, but removes the newly added transport through sctp_assoc_del_nonprimary_peers(). The removal does not clear asoc->new_transport, leaving it pointing to the removed transport.
sctp_sf_do_asconf() then creates a HEARTBEAT whose chunk->transport points to the removed transport without holding a transport reference. During local address replacement, src_out_of_asoc_ok keeps this HEARTBEAT on control_chunk_list. After the transport is freed by RCU, a successful ASCONF_ACK for the replacement address releases the queued HEARTBEAT and sctp_outq_select_transport() reads the freed transport's state.
The issue was found during a static audit of SCTP objects. With an authenticated peer, the reproducer triggered the same KASAN report in 2 of 2 unpatched runs on a KASAN-enabled netdev/main kernel:
BUG: KASAN: slab-use-after-free in sctp_outq_select_transport Read of size 4 at addr ffff88800b9bd95c by task python3/197
Call Trace: sctp_outq_select_transport+0x549/0x8b0 [sctp]
sctp_outq_flush+0x306/0x2c60 [sctp]
sctp_transport_immediate_rtx+0xaf/0x260 [sctp]
sctp_process_asconf_ack+0xa48/0xf70 [sctp]
Allocated by task 197: sctp_transport_new+0x68/0x650 [sctp]
sctp_assoc_add_peer+0x258/0x12a0 [sctp]
sctp_process_asconf+0x5e9/0x1090 [sctp]
Last potentially related work creation: __call_rcu_common.constprop.0+0x77/0xb70 sctp_assoc_del_nonprimary_peers+0x7c/0xd0 [sctp]
sctp_process_asconf+0xd9c/0x1090 [sctp]
The first invalid access was a four-byte read of transport->state at net/sctp/outqueue.c:833. The same reproducer completed the full authenticated ASCONF and local-address replacement sequence with this change without a KASAN report or oops.
Clear new_transport when its peer is removed, before it can be used to create the HEARTBEAT.
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Analysis
by VulDB Data Team • 08/22/2026
The vulnerability identified in the Linux kernel's Stream Control Transmission Protocol (SCTP) implementation involves a use-after-free condition within the sctp_sf_do_asconf function. This flaw arises from improper state management when handling Address Configuration Change (ASCONF) chunks, specifically during scenarios where a remote peer adds and subsequently removes an IP address transport within a single authenticated message sequence. The core technical issue lies in the lifecycle of the asoc->new_transport pointer, which is utilized to initiate heartbeats for newly added transports but fails to be nullified when that transport is concurrently removed via wildcard deletion parameters.
The operational mechanism begins when sctp_process_asconf_param processes an ASCONF chunk and stores a reference to a newly added peer transport in the asoc->new_transport field. Under normal circumstances, this pointer remains valid until the heartbeat transmission completes or the association terminates. However, if the same authenticated ASCONF chunk includes a wildcard DEL-IP parameter that removes all non-primary peers including the one just added, the function sctp_assoc_del_nonprimary_peers is invoked to dismantle the transport structure. Crucially, while this removal process frees the underlying memory associated with the transport object using Read-Copy Update (RCU) mechanisms for asynchronous cleanup, it neglects to clear the asoc->new_transport pointer. This leaves a dangling reference pointing to memory that may be reclaimed and reallocated for other purposes or marked as invalid by kernel debugging tools like KASAN.
Following the processing of all parameters in the ASCONF chunk, sctp_sf_do_asconf attempts to send a HEARTBEAT probe to verify reachability on the new transport. It retrieves the pointer from asoc->new_transport without verifying its validity or holding an additional reference count that would prevent premature deallocation. Because the transport has already been scheduled for deletion and potentially freed by RCU, this action results in reading stale memory. Specifically, sctp_outq_select_transport performs a four-byte read of the transport's state field at net/sctp/outqueue.c:833. If the underlying slab object has been reallocated or is being cleaned up, this access constitutes a use-after-free vulnerability that can lead to kernel panics, information disclosure through leaked memory contents, or potentially arbitrary code execution if an attacker can control the data written into the reclaimed slab region.
The impact of this vulnerability is significant for systems relying on SCTP for reliable network communication, particularly in environments where authenticated peers are permitted to modify association parameters dynamically. An authenticated remote peer can trigger this condition by crafting a malicious ASCONF chunk that adds and deletes an IP address simultaneously. The exploitability depends on the timing of RCU callbacks and memory allocation patterns, but successful exploitation could destabilize the kernel or compromise system integrity. The vulnerability was detected during static audits and confirmed via KASAN-enabled testing, which consistently reproduced slab-use-after-free errors in unpatched kernels, highlighting the deterministic nature of this race condition under specific network configurations involving local address replacement sequences.
From a standards perspective, this flaw aligns with CWE-416: Use After Free, as it involves accessing memory after it has been freed without proper synchronization or reference counting safeguards. In terms of adversarial tactics, this vulnerability relates to ATT&CK techniques involving exploitation of software vulnerabilities for denial of service or potential privilege escalation if the kernel state is manipulated further through subsequent interactions. The lack of validation on pointer validity before dereference represents a fundamental security logic error in protocol handling code.
Mitigation strategies primarily involve applying vendor-provided patches that address this specific defect by ensuring asoc->new_transport is cleared to NULL immediately after sctp_assoc_del_nonprimary_peers executes if the transport being removed matches the new transport reference. This prevents subsequent functions from accessing invalid memory addresses. Administrators should ensure their Linux kernels are updated with security fixes addressing SCTP state management issues. Additionally, network segmentation and strict authentication policies for SCTP peers can reduce the attack surface by limiting which entities can send ASCONF commands that trigger complex peer addition and removal sequences. Monitoring kernel logs for KASAN reports or unusual SCTP association terminations may also aid in detecting attempted exploitation of this flaw before it causes system instability.