high CVSS 7.8

CVE-2025-21704·Kernel vulnerability

In the Linux kernel, the following vulnerability has been resolved: usb: cdc-acm: Check control transfer buffer size before access If the first fragment is shorter than struct usb_cdc_notification, we can't calculate an expected_size. Log an error and discard the notification instead of reading lengths from memory outside the received data, which can lead to memory corruption when the expected_size decreases between fragments, causing `expected_size - acm->nb_index` to wrap. This issue has been present since the beginning of git history; however, it only leads to memory corruption since commit ea2583529cd1 ("cdc-acm: reassemble fragmented notifications"). A mitigating factor is that acm_ctrl_irq() can only execute after userspace has opened /dev/ttyACM*; but if ModemManager is running, ModemManager will do that automatically depending on the USB device's vendor/product IDs and its other interfaces.

Severity
high
Software
Kernel
Fixed in
6.13.4
Published
2025-02-22

Affected versions

From: 6.13

Until: 6.13.4

Fixed in: 6.13.4

How to fix this CVE

Update your Linux kernel to version 6.13.4 or later to resolve a buffer boundary validation flaw in the USB CDC-ACM driver that could lead to memory corruption. This vulnerability affects kernel versions 6.13 through 6.13.3 and requires a kernel upgrade followed by a system reboot to take effect.

sudo dnf update kernel kernel-devel && sudo reboot

Defensia detects this vulnerability

How to check if you are affected

  1. Check installed kernel version with: uname -r (compare against affected range 6.13.x)
  2. Verify CDC-ACM driver is loaded with: lsmod | grep cdc_acm (confirms vulnerable component is active)
  3. Check kernel logs for buffer-related warnings: sudo dmesg | grep -i 'cdc\|acm\|buffer\|corruption'
  4. Confirm patch installation by checking kernel release date: uname -v (must show 6.13.4 or later)

FAQ

What is CVE-2025-21704?

A buffer size validation vulnerability in the Linux kernel's USB CDC-ACM driver that fails to verify control transfer buffer lengths before accessing them, allowing memory corruption when fragmented notifications are reassembled with inconsistent expected sizes.

Is CVE-2025-21704 being actively exploited?

No, this vulnerability is not currently listed in the CISA Known Exploited Vulnerabilities catalog and no public exploits are available, though local privilege escalation is theoretically possible if ModemManager automatically opens /dev/ttyACM* on affected systems.

What versions of Kernel are affected by CVE-2025-21704?

Linux kernel versions 6.13.0 through 6.13.3 are vulnerable; the fix is included in kernel 6.13.4 and all subsequent releases.

How do I check if my server is vulnerable to CVE-2025-21704?

Run 'uname -r' and verify the kernel version is between 6.13.0 and 6.13.3; additionally check 'lsmod | grep cdc_acm' to confirm the vulnerable driver is loaded.

Does Defensia detect CVE-2025-21704?

Yes — Defensia's CVE advisory scanner compares installed kernel package versions against the NVD database. If a vulnerable kernel version is detected on a monitored server, CVE-2025-21704 will appear in your dashboard with remediation steps and impact assessment.

Related Kernel CVEs

CVE-2024-42256CVSS 9.8In the Linux kernel, the following vulnerability has been resolved: cifs: Fix server re-repick on subrequest retry When a subrequest is marked for needing retry, netfs will call cifs_prepare_write() which will make cifs repick the server for the op before renegotiating credits; it then calls cifs_issue_write() which invokes smb2_async_writev() - which re-repicks the server. If a different server is then selected, this causes the increment of server->in_flight to happen against one record and the decrement to happen against another, leading to misaccounting. Fix this by just removing the repick code in smb2_async_writev(). As this is only called from netfslib-driven code, cifs_prepare_write() should always have been called first, and so server should never be NULL and the preparatory step is repeated in the event that we do a retry. The problem manifests as a warning looking something like: WARNING: CPU: 4 PID: 72896 at fs/smb/client/smb2ops.c:97 smb2_add_credits+0x3f0/0x9e0 [cifs] ... RIP: 0010:smb2_add_credits+0x3f0/0x9e0 [cifs] ... smb2_writev_callback+0x334/0x560 [cifs] cifs_demultiplex_thread+0x77a/0x11b0 [cifs] kthread+0x187/0x1d0 ret_from_fork+0x34/0x60 ret_from_fork_asm+0x1a/0x30 Which may be triggered by a number of different xfstests running against an Azure server in multichannel mode. generic/249 seems the most repeatable, but generic/215, generic/249 and generic/308 may also show it.
CVE-2024-36031CVSS 9.8In the Linux kernel, the following vulnerability has been resolved: keys: Fix overwrite of key expiration on instantiation The expiry time of a key is unconditionally overwritten during instantiation, defaulting to turn it permanent. This causes a problem for DNS resolution as the expiration set by user-space is overwritten to TIME64_MAX, disabling further DNS updates. Fix this by restoring the condition that key_set_expiry is only called when the pre-parser sets a specific expiry.
CVE-2024-38612CVSS 9.8In the Linux kernel, the following vulnerability has been resolved: ipv6: sr: fix invalid unregister error path The error path of seg6_init() is wrong in case CONFIG_IPV6_SEG6_LWTUNNEL is not defined. In that case if seg6_hmac_init() fails, the genl_unregister_family() isn't called. This issue exist since commit 46738b1317e1 ("ipv6: sr: add option to control lwtunnel support"), and commit 5559cea2d5aa ("ipv6: sr: fix possible use-after-free and null-ptr-deref") replaced unregister_pernet_subsys() with genl_unregister_family() in this error path.
CVE-2024-38623CVSS 9.8In the Linux kernel, the following vulnerability has been resolved: fs/ntfs3: Use variable length array instead of fixed size Should fix smatch warning: ntfs_set_label() error: __builtin_memcpy() 'uni->name' too small (20 vs 256)
CVE-2021-47548CVSS 9.8In the Linux kernel, the following vulnerability has been resolved: ethernet: hisilicon: hns: hns_dsaf_misc: fix a possible array overflow in hns_dsaf_ge_srst_by_port() The if statement: if (port >= DSAF_GE_NUM) return; limits the value of port less than DSAF_GE_NUM (i.e., 8). However, if the value of port is 6 or 7, an array overflow could occur: port_rst_off = dsaf_dev->mac_cb[port]->port_rst_off; because the length of dsaf_dev->mac_cb is DSAF_MAX_PORT_NUM (i.e., 6). To fix this possible array overflow, we first check port and if it is greater than or equal to DSAF_MAX_PORT_NUM, the function returns.

References

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