medium CVSS 5.5 EPSS <0.1%

CVE-2021-47392·Kernel vulnerability

In the Linux kernel, the following vulnerability has been resolved: RDMA/cma: Fix listener leak in rdma_cma_listen_on_all() failure If cma_listen_on_all() fails it leaves the per-device ID still on the listen_list but the state is not set to RDMA_CM_ADDR_BOUND. When the cmid is eventually destroyed cma_cancel_listens() is not called due to the wrong state, however the per-device IDs are still holding the refcount preventing the ID from being destroyed, thus deadlocking: task:rping state:D stack: 0 pid:19605 ppid: 47036 flags:0x00000084 Call Trace: __schedule+0x29a/0x780 ? free_unref_page_commit+0x9b/0x110 schedule+0x3c/0xa0 schedule_timeout+0x215/0x2b0 ? __flush_work+0x19e/0x1e0 wait_for_completion+0x8d/0xf0 _destroy_id+0x144/0x210 [rdma_cm] ucma_close_id+0x2b/0x40 [rdma_ucm] __destroy_id+0x93/0x2c0 [rdma_ucm] ? __xa_erase+0x4a/0xa0 ucma_destroy_id+0x9a/0x120 [rdma_ucm] ucma_write+0xb8/0x130 [rdma_ucm] vfs_write+0xb4/0x250 ksys_write+0xb5/0xd0 ? syscall_trace_enter.isra.19+0x123/0x190 do_syscall_64+0x33/0x40 entry_SYSCALL_64_after_hwframe+0x44/0xa9 Ensure that cma_listen_on_all() atomically unwinds its action under the lock during error.

Severity
medium
Software
Kernel
Fixed in
5.14.10
Published

How likely is exploitation

FIRST's Exploit Prediction Scoring System puts the probability of this CVE being exploited in the next 30 days at <0.1% — higher than 3% of all published CVEs. EPSS is an independent forecast of exploitation, not a severity rating: it says nothing about how much damage a successful attack does, which is what a CVSS score measures.

Affected versions

From: 5.11

Until: 5.14.10

Fixed in: 5.14.10

How to fix this CVE

Update the Linux kernel to version 5.14.10 or later to resolve a resource cleanup issue in the RDMA connection management subsystem. This vulnerability causes listener objects to remain improperly referenced during error conditions, potentially leading to system deadlocks. Apply the kernel update through your distribution's package manager and reboot the system to complete the remediation.

sudo dnf update kernel && sudo reboot

Defensia detects this vulnerability

How to check if you are affected

  1. Check current kernel version: uname -r (compare against 5.14.10 baseline; vulnerable if 5.11.x through 5.14.9)
  2. Verify RDMA subsystem presence: lsmod | grep rdma (presence indicates the vulnerable code path is loaded)
  3. Monitor for hung task warnings: grep -i 'task.*state:D' /var/log/kern.log or dmesg | grep -i 'hung_task' (indicators of deadlock from listener leak)
  4. Confirm remediation applied: uname -r should show 5.14.10 or later, and dmesg should not show hung task detection for RDMA operations

FAQ

What is CVE-2021-47392?

This vulnerability affects the Linux kernel's RDMA connection management layer (cma_listen_on_all function). When listener setup fails, cleanup routines skip executing due to incorrect state tracking, leaving reference counts elevated and causing system deadlocks during connection destruction.

Is CVE-2021-47392 being actively exploited?

No, this vulnerability is not listed in the CISA Known Exploited Vulnerabilities catalog and no public exploits are currently available. It requires local access and specific RDMA subsystem usage to trigger.

What versions of Kernel are affected by CVE-2021-47392?

Linux kernel versions 5.11.0 through 5.14.9 are vulnerable. Version 5.14.10 and later include the fix.

How do I check if my server is vulnerable to CVE-2021-47392?

Run 'uname -r' and check if the output is between 5.11.0 and 5.14.9. If your kernel version falls within this range and RDMA modules are loaded (lsmod | grep rdma), your system is vulnerable.

Does Defensia detect CVE-2021-47392?

Yes — Defensia's CVE advisory scanner compares installed package versions against the NVD database. If the Linux kernel is installed on a monitored server, CVE-2021-47392 will appear in your dashboard with remediation steps.

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References

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