Summary
In the Linux kernel, the following vulnerability has been resolved: openvswitch: fix lockup on...
In the Linux kernel, the following vulnerability has been resolved:
openvswitch: fix lockup on tx to unregistering netdev with carrier
Commit in a fixes tag attempted to fix the issue in the following
sequence of calls:
do_output
-> ovs_vport_send
-> dev_queue_xmit
-> __dev_queue_xmit
-> netdev_core_pick_tx
-> skb_tx_hash
When device is unregistering, the 'dev->real_num_tx_queues' goes to
zero and the 'while (unlikely(hash >= qcount))' loop inside the
'skb_tx_hash' becomes infinite, locking up the core forever.
But unfortunately, checking just the carrier status is not enough to
fix the issue, because some devices may still be in unregistering
state while reporting carrier status OK.
One example of such device is a net/dummy. It sets carrier ON
on start, but it doesn't implement .ndo_stop to set the carrier off.
And it makes sense, because dummy doesn't really have a carrier.
Therefore, while this device is unregistering, it's still easy to hit
the infinite loop in the skb_tx_hash() from the OVS datapath. There
might be other drivers that do the same, but dummy by itself is
important for the OVS ecosystem, because it is frequently used as a
packet sink for tcpdump while debugging OVS deployments. And when the
issue is hit, the only way to recover is to reboot.
Fix that by also checking if the device is running. The running
state is handled by the net core during unregistering, so it covers
unregistering case better, and we don't really need to send packets
to devices that are not running anyway.
While only checking the running state might be enough, the carrier
check is preserved. The running and the carrier states seem disjoined
throughout the code and different drivers. And other core functions
like __dev_direct_xmit() check both before attempting to transmit
a packet. So, it seems safer to check both flags in OVS as well.
Impact
CVE-2025-21681 has a CVSS score of 5.5 (Medium). The vector is requires local access, low privileges required, and no user interaction. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment. No fixed version is listed yet, so configuration controls and monitoring matter more in the interim.
Affected versions
Security releases
Kodem intelligence
Severity tells you how bad this could be in the worst case. It does not tell you whether you are exposed. Exploitability and impact are functions of runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A vulnerable package can sit in your dependency tree and never run.
Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter. Kodem's runtime-powered SCA identifies whether this CVE is reachable in your applications.
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Frequently Asked Questions
- What is CVE-2025-21681? CVE-2025-21681 is a medium-severity security vulnerability. No fixed version is listed yet.
- How severe is CVE-2025-21681? CVE-2025-21681 has a CVSS score of 5.5 (Medium). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
- Is there a fix for CVE-2025-21681? No fixed version is listed for CVE-2025-21681 yet. Monitor the advisory for updates and apply mitigations in the interim.
- Is CVE-2025-21681 exploitable, and should I be worried? Whether CVE-2025-21681 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
- What actually determines whether CVE-2025-21681 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.