high CVSS 7.8 Actively exploited EPSS 1.3%

CVE-2025-39964·Kernel vulnerability

In the Linux kernel, the following vulnerability has been resolved: crypto: af_alg - Disallow concurrent writes in af_alg_sendmsg Issuing two writes to the same af_alg socket is bogus as the data will be interleaved in an unpredictable fashion. Furthermore, concurrent writes may create inconsistencies in the internal socket state. Disallow this by adding a new ctx->write field that indiciates exclusive ownership for writing.

Severity
high
Software
Kernel
Fixed in
6.16.9
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 1.3% — higher than 69% 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: 6.13

Until: 6.16.9

Fixed in: 6.16.9

How to fix this CVE

Update your Linux kernel to version 6.16.9 or later to patch the af_alg socket write concurrency vulnerability. This fix enforces exclusive write access to af_alg sockets, preventing data interleaving and internal state corruption that could result from simultaneous write operations. Apply the update immediately as this vulnerability is actively exploited in the wild.

sudo dnf update kernel kernel-devel && sudo reboot

Defensia detects this vulnerability

How to check if you are affected

  1. Check your current kernel version: uname -r
  2. Verify if af_alg module is loaded: lsmod | grep af_alg
  3. Review dmesg logs for af_alg-related errors: dmesg | grep -i af_alg
  4. After patching, confirm the new kernel version boots: uname -r should show 6.16.9 or later

FAQ

What is CVE-2025-39964?

CVE-2025-39964 is a kernel vulnerability in the AF_ALG socket subsystem that allows concurrent write operations to corrupt the socket's internal state and interleave cryptographic data. The vulnerability stems from missing mutual exclusion controls that should serialize write operations.

Is CVE-2025-39964 being actively exploited?

Yes, CVE-2025-39964 is listed in the CISA Known Exploited Vulnerabilities (KEV) catalog, indicating active exploitation in the wild. No public exploit code has been disclosed, but threat actors have demonstrated practical attacks.

What versions of Kernel are affected by CVE-2025-39964?

Linux kernel versions 6.13 through 6.16.8 are vulnerable. Kernel 6.16.9 and later versions contain the fix that adds the ctx->write mutual exclusion field.

How do I check if my server is vulnerable to CVE-2025-39964?

Run 'uname -r' to display your kernel version. If the output shows 6.13.x through 6.16.8, your system is vulnerable. Additionally, check if af_alg is enabled: grep -i af_alg /boot/config-$(uname -r)

Does Defensia detect CVE-2025-39964?

Yes — Defensia's CVE advisory scanner compares installed kernel versions against the NVD database. If a vulnerable kernel version is detected on a monitored server, CVE-2025-39964 will appear in your dashboard with remediation steps and priority alerts.

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CVE-2026-64125CVSS 9.8In the Linux kernel, the following vulnerability has been resolved: net: bcmgenet: keep RBUF EEE/PM disabled Setting RBUF_EEE_EN | RBUF_PM_EN in RBUF_ENERGY_CTRL breaks the RX path on GENET hardware once MAC EEE becomes active. RX traffic stops flowing while the link stays up and the usual descriptor/RX error counters remain quiet. In that state the MAC still accepts frames (rbuf_ovflow_cnt keeps climbing) but RBUF no longer forwards them to DMA, so rx_packets is no longer incremented at the netdev level. On some boards the corruption ends up as a paging fault in skb_release_data via bcmgenet_rx_poll on an LPI exit. Reproduced on Pi 4B (BCM2711 + BCM54213PE) and confirmed by Florian Fainelli on an internal Broadcom 4908-family board with the same crash signature. RBUF_PM_EN is not publicly documented. This shows up more often now that phy_support_eee() enables EEE by default, but it also affects older kernels as soon as TX LPI is turned on via ethtool, so it is not specific to recent changes. Always clear RBUF_EEE_EN | RBUF_PM_EN in bcmgenet_eee_enable_set so the bits stay off across resets. UMAC and TBUF setup is left alone so TX-side EEE keeps working.
CVE-2026-64136CVSS 9.8In the Linux kernel, the following vulnerability has been resolved: smb: client: protect tc_count increment in smb2_find_smb_sess_tcon_unlocked() Commit 96c4af418586 ("cifs: Fix locking usage for tcon fields") refactored cifs code to change cifs_tcp_ses_lock for tc_lock around tc_count changes. There was missing lock around tc_count increment inside smb2_find_smb_sess_tcon_unlocked().
CVE-2026-53399CVSS 9.8In the Linux kernel, the following vulnerability has been resolved: nfsd: release layout stid on setlease failure nfs4_alloc_stid() publishes the new stid into cl->cl_stateids via idr_alloc_cyclic() under cl_lock before returning to nfsd4_alloc_layout_stateid(). When nfsd4_layout_setlease() then fails, the error path frees the layout stateid directly with kmem_cache_free() without ever calling idr_remove(), leaving the IDR slot pointing at freed slab memory. Any subsequent IDR walker (states_show, client teardown) dereferences the dangling pointer. The correct teardown for an IDR-published stid is nfs4_put_stid(), which removes the IDR slot under cl_lock, dispatches sc_free (nfsd4_free_layout_stateid) to release ls->ls_file via nfsd4_close_layout(), and drops the nfs4_file reference in its tail. A second issue blocks that switch: nfsd4_free_layout_stateid() unconditionally inspects ls->ls_fence_work via delayed_work_pending() under ls_lock, but INIT_DELAYED_WORK(&ls->ls_fence_work, ...) currently runs only after the setlease call. On the setlease-failure path the destructor would touch an uninitialized delayed_work. nfsd4_alloc_layout_stateid() nfs4_alloc_stid() /* idr_alloc_cyclic under cl_lock */ nfsd4_layout_setlease() /* fails */ nfs4_put_stid() nfsd4_free_layout_stateid() delayed_work_pending(&ls->ls_fence_work) /* needs INIT */ nfsd4_close_layout() /* nfsd_file_put(ls->ls_file) */ put_nfs4_file() Fix by hoisting the ls_fenced / ls_fence_delay / INIT_DELAYED_WORK initialization above the nfsd4_layout_setlease() call, and replace the manual nfsd_file_put + put_nfs4_file + kmem_cache_free cleanup with a single nfs4_put_stid(stp).

References

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