Reference page — cumulative record through Monday, October 19, 2026 UTC. Reference pages update as the archive grows; only dated daily editions are immutable pages of record.
CVE-2025-21704
Linux Linux — usb: cdc-acm: Check control transfer buffer size before access
AV AC PR UI S C I A CVSS EPSS %ile KEV
L L L N U H H H 7.8 .0037 29.1 —
AFFECTED
Product Versions Fixed
Linux 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 – —
Linux 2.6.12 – 5.4.291
TIMELINE
Dec 29 Reserved by Linux
Feb 22 Published (CNA: Linux)
Oct 15 ENRICHED — CVE-2025-21704 (Linux). Received CVSS 7.8 and CPE data from NVD.
Oct 15 EXPLOIT PUBLISHED — CVE-2025-21704 (Linux). Public exploit reference added.
Description
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.
Lifecycle
Complete event history — 4 events, chronological
| Date | Event | Detail |
|---|
| December 29, 2024 | Reserved | Reserved by Linux |
| February 22, 2025 | Published | Published (CNA: Linux) |
| October 15, 2026 | ENRICHED | ENRICHED — CVE-2025-21704 (Linux). Received CVSS 7.8 and CPE data from NVD. |
| October 15, 2026 | EXPLOIT PUBLISHED | EXPLOIT PUBLISHED — CVE-2025-21704 (Linux). Public exploit reference added. |
Affected
Affected products and packages — 2 rows
| Vendor | Product / Package | Ecosystem | Version introduced | Fixed |
|---|
| Linux | Linux | — | 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 | — |
| Linux | Linux | — | 2.6.12 | 5.4.291 |
About this page
This is a reference page, not a dated page of record. It assembles the complete lifecycle of CVE-2025-21704 from the CVE Program record, NVD enrichment, the CISA KEV catalog, EPSS, and OSV advisories. The box score's numbers (CVSS, EPSS, KEV status) are current as of Monday, October 19, 2026 UTC and are re-derived as the archive grows; only dated daily editions are immutable pages of record. The authoritative source for this identifier is cve.org.
