CVE-2025-21704 | usb: cdc-acm: Check control transfer buffer size before access

Exp

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.

Published: 2025-02-22 Last update: 2026-05-12 Assigner: 416baaa9-dc9f-4396-8d5f-8c081fb06d67 Source: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
NVD Status：Modified，CVE State: published
View at NVD, CVE.org, EUVD

CVE-2025-21704 is rated Exploit Available (50.5/100): CVSS High severity, with low exploitation likelihood (EPSS 0.04%). 1 public exploit reference(s) are indexed (Exploit-DB). Public exploits are available—assess exposure, apply mitigations, and prioritize patching.

Risk is dynamic; we continuously reassess and refresh what is shown on this page as upstream context changes.

Public exploit references (Exploit-DB) for CVE-2025-21704

EDB-ID Source Kind Published Link
— nvd_ref exploit_tag Exploit-DB ↗

Exploit prediction scoring system (EPSS) score for CVE-2025-21704

EPSS lead: Daily EPSS estimates relative likelihood of exploitation; percentile ranks this CVE among scored vulnerabilities (higher = more severe relative rank).

# Date Old EPSS score New EPSS score Delta (New - Old)
1 2025-12-28 0.05% 0.04% -0.01%
2 2025-12-27 0.04% 0.05% +0.01%
3 2025-11-21 — 0.04% —

Full EPSS history (8 records total)

Common vulnerability scoring system (CVSS) metrics for CVE-2025-21704

CVSS metrics for this CVE.

Base score Version Severity Vector Exploitability Impact Score source
7.8 3.1 HIGH
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H Click to expand
Attack vector (AV:L)
They already need access on the box, or another person has to do something wrong; it’s not a remote drive-by.
Attack complexity (AC:L)
Once they can reach the bug, pulling it off is straightforward—no weird race conditions or rare setup.
Privileges required (PR:L)
A normal user session is enough; they don’t have to be admin.
User interaction (UI:N)
Nobody has to click “OK” or open a trap file; it can work without a victim helping.
Scope (S:U)
Damage stays in the same “trust bubble” as the broken component—no big spill into unrelated systems.
Confidentiality (C:H)
Serious risk that confidential data gets exposed in a big way.
Integrity (I:H)
They could widely tamper with or forge data—trust in the data is badly hurt.
Availability (A:H)
Could take the service down hard or make it unusable for people who depend on it.
 1.8 5.9 [email protected]

Weakness enumeration for CVE-2025-21704

GitHub Security Advisory for CVE-2025-21704

GHSA-48g3-w2gf-xjrv · Severity: high — In the Linux kernel, the following vulnerability has been resolved: usb: cdc-acm: Check control...

OS Trackers for CVE-2025-21704

vendor priority summary link
debian not yet assigned CVE-2025-21704 not yet assigned priority: Debian including 2 source packages (linux, linux-6.1), 6 status rows across 5 suites (bookworm, bullseye, forky, sid, trixie): resolved 6. https://security-tracker.debian.org/tracker/CVE-2025-21704
redhat medium — https://access.redhat.com/security/cve/CVE-2025-21704
suse medium CVE-2025-21704 severity moderate: SUSE including 432 source package names (2.1.3-6.11:kernel-default-6.4.0-28.1, 2.1.3-6.12:kernel-default-base-6.4.0-28.1.21.6, …), 709 product×package rows across 127 product lines (Container suse/sl-micro/6.0/base-os-container, Container suse/sl-micro/6.0/kvm-os-container, … (127 product lines)): Fixed 438, Known Affected 231, Known Not Affected 40. https://www.suse.com/security/cve/CVE-2025-21704/
ubuntu high CVE-2025-21704 high priority: Ubuntu including 158 source packages (linux, linux-allwinner-5.19, …), 1551 status rows across 10 suites (bionic, focal, jammy, noble, oracular, plucky, questing, trusty, upstream, xenial): DNE 1145, released 211, ignored 150, not-affected 43, needed 2. https://ubuntu.com/security/CVE-2025-21704

Affected software / configurations for CVE-2025-21704

Vendor Product Version Raw CPE
linux linux_kernel >= 2.6.13, < 5.4.291 cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*
linux linux_kernel >= 5.5, < 5.10.235 cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*
linux linux_kernel >= 5.11, < 5.15.179 cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*
linux linux_kernel >= 5.16, < 6.1.129 cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*
linux linux_kernel >= 6.2, < 6.6.79 cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*
linux linux_kernel >= 6.7, < 6.12.16 cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*
linux linux_kernel >= 6.13, < 6.13.4 cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*
linux linux_kernel 2.6.12 cpe:2.3:o:linux:linux_kernel:2.6.12:-:*:*:*:*:*:*
linux linux_kernel 2.6.12 cpe:2.3:o:linux:linux_kernel:2.6.12:rc2:*:*:*:*:*:*
linux linux_kernel 2.6.12 cpe:2.3:o:linux:linux_kernel:2.6.12:rc3:*:*:*:*:*:*
linux linux_kernel 2.6.12 cpe:2.3:o:linux:linux_kernel:2.6.12:rc4:*:*:*:*:*:*
linux linux_kernel 2.6.12 cpe:2.3:o:linux:linux_kernel:2.6.12:rc5:*:*:*:*:*:*
linux linux_kernel 6.14 cpe:2.3:o:linux:linux_kernel:6.14:rc1:*:*:*:*:*:*
linux linux_kernel 6.14 cpe:2.3:o:linux:linux_kernel:6.14:rc2:*:*:*:*:*:*

References for CVE-2025-21704

URL Tags
https://git.kernel.org/stable/c/383d516a0ebc8641372b521c8cb717f0f1834831 Patch
https://git.kernel.org/stable/c/6abb510251e75f875797d8983a830e6731fa281c Patch
https://git.kernel.org/stable/c/7828e9363ac4d23b02419bf2a45b9f1d9fb35646 Patch
https://git.kernel.org/stable/c/871619c2b78fdfe05afb4e8ba548678687beb812 Patch
https://git.kernel.org/stable/c/90dd2f1b7342b9a671a5ea4160f408037b92b118 Patch
https://git.kernel.org/stable/c/a4e1ae5c0533964170197e4fb4f33bc8c1db5cd2 Patch
https://git.kernel.org/stable/c/e563b01208f4d1f609bcab13333b6c0e24ce6a01 Patch
https://git.kernel.org/stable/c/f64079bef6a8a7823358c3f352ea29a617844636 Patch
https://project-zero.issues.chromium.org/issues/395107243 Exploit Issue Tracking Third Party Advisory
https://lists.debian.org/debian-lts-announce/2025/03/msg00028.html
https://lists.debian.org/debian-lts-announce/2025/05/msg00030.html
https://cert-portal.siemens.com/productcert/html/ssa-265688.html
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