CVE-2024-57974 in Linux
Summary
by MITRE • 02/27/2025
In the Linux kernel, the following vulnerability has been resolved:
udp: Deal with race between UDP socket address change and rehash
If a UDP socket changes its local address while it's receiving datagrams, as a result of connect(), there is a period during which a lookup operation might fail to find it, after the address is changed but before the secondary hash (port and address) and the four-tuple hash (local and remote ports and addresses) are updated.
Secondary hash chains were introduced by commit 30fff9231fad ("udp: bind() optimisation") and, as a result, a rehash operation became needed to make a bound socket reachable again after a connect().
This operation was introduced by commit 719f835853a9 ("udp: add rehash on connect()") which isn't however a complete fix: the socket will be found once the rehashing completes, but not while it's pending.
This is noticeable with a socat(1) server in UDP4-LISTEN mode, and a client sending datagrams to it. After the server receives the first datagram (cf. _xioopen_ipdgram_listen()), it issues a connect() to the address of the sender, in order to set up a directed flow.
Now, if the client, running on a different CPU thread, happens to send a (subsequent) datagram while the server's socket changes its address, but is not rehashed yet, this will result in a failed lookup and a port unreachable error delivered to the client, as apparent from the following reproducer:
LEN=$(($(cat /proc/sys/net/core/wmem_default) / 4)) dd if=/dev/urandom bs=1 count=${LEN} of=tmp.in
while :; do taskset -c 1 socat UDP4-LISTEN:1337,null-eof OPEN:tmp.out,create,trunc & sleep 0.1 || sleep 1 taskset -c 2 socat OPEN:tmp.in UDP4:localhost:1337,shut-null wait done
where the client will eventually get ECONNREFUSED on a write() (typically the second or third one of a given iteration):
2024/11/13 21:28:23 socat[46901] E write(6, 0x556db2e3c000, 8192): Connection refused
This issue was first observed as a seldom failure in Podman's tests checking UDP functionality while using pasta(1) to connect the container's network namespace, which leads us to a reproducer with the lookup error resulting in an ICMP packet on a tap device:
LOCAL_ADDR="$(ip -j -4 addr show|jq -rM '.[] | .addr_info[0] | select(.scope == "global").local')"
while :; do ./pasta --config-net -p pasta.pcap -u 1337 socat UDP4-LISTEN:1337,null-eof OPEN:tmp.out,create,trunc & sleep 0.2 || sleep 1 socat OPEN:tmp.in UDP4:${LOCAL_ADDR}:1337,shut-null
wait cmp tmp.in tmp.out done
Once this fails:
tmp.in tmp.out differ: char 8193, line 29
we can finally have a look at what's going on:
$ tshark -r pasta.pcap 1 0.000000 :: ? ff02::16 ICMPv6 110 Multicast Listener Report Message v2 2 0.168690 88.198.0.161 ? 88.198.0.164 UDP 8234 60260 ? 1337 Len=8192 3 0.168767 88.198.0.161 ? 88.198.0.164 UDP 8234 60260 ? 1337 Len=8192 4 0.168806 88.198.0.161 ? 88.198.0.164 UDP 8234 60260 ? 1337 Len=8192 5 0.168827 c6:47:05:8d:dc:04 ? Broadcast ARP 42 Who has 88.198.0.161? Tell 88.198.0.164 6 0.168851 9a:55:9a:55:9a:55 ? c6:47:05:8d:dc:04 ARP 42 88.198.0.161 is at 9a:55:9a:55:9a:55 7 0.168875 88.198.0.161 ? 88.198.0.164 UDP 8234 60260 ? 1337 Len=8192 8 0.168896 88.198.0.164 ? 88.198.0.161 ICMP 590 Destination unreachable (Port unreachable) 9 0.168926 88.198.0.161 ? 88.198.0.164 UDP 8234 60260 ? 1337 Len=8192 10 0.168959 88.198.0.161 ? 88.198.0.164 UDP 8234 60260 ? 1337 Len=8192 11 0.168989 88.198.0.161 ? 88.198.0.164 UDP 4138 60260 ? 1337 Len=4096 12 0.169010 88.198.0.161 ? 88.198.0.164 UDP 42 60260 ? 1337 Len=0
On the third datagram received, the network namespace of the container initiates an ARP lookup to deliver the ICMP message.
In another variant of this reproducer, starting the client with:
strace -f pasta --config-net -u 1337 socat UDP4-LISTEN:1337,null-eof OPEN:tmp.out,create,tru ---truncated---
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Analysis
by VulDB Data Team • 05/24/2026
The vulnerability described in CVE-2024-57974 resides within the Linux kernel's UDP implementation and stems from a race condition during socket address changes. This flaw occurs when a UDP socket undergoes a local address modification through a connect() operation, creating a window where lookup operations fail to locate the socket due to incomplete hash table updates. The race condition arises because the secondary hash chain, introduced in commit 30fff9231fad as part of a bind() optimization, requires a rehash operation to make the socket reachable again after a connect(). However, this rehashing process, implemented in commit 719f835853a9, is not fully synchronized with the socket address change, leading to a temporary inconsistency in the socket lookup mechanism. The issue manifests when a UDP socket receives datagrams while transitioning its address, causing lookup failures that result in ICMP port unreachable messages being sent to the sender, effectively breaking communication.
The technical root cause of this vulnerability aligns with CWE-362, which describes a race condition in concurrent programming where the execution order of threads affects program behavior. The problem specifically affects UDP socket operations and is exacerbated by the interaction between the socket's address change and hash table reorganization. The race condition is particularly pronounced in multi-threaded environments where one CPU core handles the socket address modification while another processes incoming datagrams. The Linux kernel's UDP implementation uses both secondary hash chains and four-tuple hash structures for socket lookup, and the timing mismatch between these data structures causes the lookup to fail temporarily. This behavior is consistent with the ATT&CK technique T1070.006, which involves the manipulation of network communications through system-level changes that affect protocol handling.
The operational impact of CVE-2024-57974 extends beyond simple network communication failures to potentially disrupt containerized applications and network services. In real-world deployments, this vulnerability can cause intermittent connection failures in UDP-based services, particularly those using tools like socat or pasta for network communication. The issue becomes more prevalent in containerized environments where network namespaces are frequently created and destroyed, as seen in the Podman test failures that initially exposed this vulnerability. Applications relying on UDP connectivity may experience sporadic ECONNREFUSED errors, leading to data loss or application instability. The vulnerability is especially problematic for real-time applications where packet loss or delayed delivery can significantly impact performance, such as VoIP, live video streaming, or gaming applications that depend on reliable UDP communication. The intermittent nature of the failure makes it particularly difficult to detect and debug in production environments, as it may only manifest under specific timing conditions or high load scenarios.
Mitigation strategies for CVE-2024-57974 require kernel-level patches that ensure proper synchronization between socket address changes and hash table updates. The fix should guarantee that socket lookups remain consistent throughout the address change process, preventing the temporary state where a socket is unreachable. System administrators should prioritize applying the latest kernel updates that contain the resolved race condition. In environments where immediate kernel updates are not feasible, operational mitigations include reducing the frequency of connect() operations on UDP sockets, implementing application-level retry logic for UDP communications, and monitoring for ICMP port unreachable messages that may indicate the vulnerability's occurrence. Network administrators should also consider implementing additional monitoring and alerting for UDP communication failures, particularly in containerized or virtualized environments where the vulnerability is more likely to manifest. The fix addresses the core issue by ensuring that the rehashing operation completes before the socket becomes available for new lookups, thereby eliminating the race condition that leads to failed UDP socket lookups.