CVE-2025-21704 — usb: cdc-acm: Check control transfer buffer size before access
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.
Who exploits it and how urgent it is
A 0–100 score combining confirmed exploitation, ransomware and APT use, public exploits, EPSS and severity.
How the score was calculated
- EPSS 0.4% (30-day exploitation probability)+4
- Technical severity (high)+6
The score orders the patch queue; it does not replace your asset context (internet exposure, criticality, compensating controls).
Triage
Is it exploited, how likely is exploitation, what does it touch, and how severe do the sources call it.
Remediation
Fixes and mitigations documented by the sources — linked to the original advisory.
- Documented patch — git.kernel.org (NIST National Vulnerability Database)
- Documented patch — git.kernel.org (NIST National Vulnerability Database)
- Documented patch — git.kernel.org (NIST National Vulnerability Database)
- Documented patch — git.kernel.org (NIST National Vulnerability Database)
- Documented patch — git.kernel.org (NIST National Vulnerability Database)
- Documented patch — git.kernel.org (NIST National Vulnerability Database)
- Documented patch — git.kernel.org (NIST National Vulnerability Database)
- Documented patch — git.kernel.org (NIST National Vulnerability Database)
First 24 hours
Ordered from the record’s own fields — exposure first, because you cannot patch what you have not found. A rule-generated starting point.
- Identify exposed assets running the affected vendor/product/version combinations (Linux Linux, Linux Linux Kernel).
- Apply the fixed version or the patch documented under Remediation.
- Search available logs for exploit probes matching the vulnerability class (memory corruption), errors and authentication anomalies.
Affected scope
Vendor, product and versions as the sources word them.
| Vendor | Product | Versions | Status | Source |
|---|---|---|---|---|
| Linux | Linux |
version 2.6.12≥ 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 and < e563b01208f4d1f609bcab13333b6c0e24ce6a01≥ 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 and < 383d516a0ebc8641372b521c8cb717f0f1834831≥ 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 and < f64079bef6a8a7823358c3f352ea29a617844636≥ 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 and < 6abb510251e75f875797d8983a830e6731fa281c≥ 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 and < 7828e9363ac4d23b02419bf2a45b9f1d9fb35646≥ 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 and < 871619c2b78fdfe05afb4e8ba548678687beb812≥ 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 and < 90dd2f1b7342b9a671a5ea4160f408037b92b118 and 1 more≥ 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 and < a4e1ae5c0533964170197e4fb4f33bc8c1db5cd2 |
Vulnerable | CVE Program (cve.org) e CISA ADP |
| Linux | Linux Kernel |
version 2.6.12-rc5version 6.14-rc2version 6.14-rc1≥ 2.6.13 and < 5.4.291version 2.6.12-rc4version 2.6.12-rc3version 2.6.12-rc2version 2.6.12 and 6 more≥ 6.13 and < 6.13.4≥ 6.7 and < 6.12.16≥ 6.2 and < 6.6.79≥ 5.16 and < 6.1.129≥ 5.11 and < 5.15.179≥ 5.5 and < 5.10.235 |
Vulnerable | NIST National Vulnerability Database |
Attack characteristics
The CVSS vector, decoded. It describes the attack, not your exposure to it.
Every base score collected
Sources score independently and may disagree; each row says who scored it and under which version.
| Score | Version | Severity | Expl. | Impact | Scored by |
|---|---|---|---|---|---|
| 7.8 | CVSS 3.1 | High | 1.8 | 5.9 | nvd@nist.gov via NIST National Vulnerability Database |
| 7.8 | CVSS 3.1 | High | — | — | GitHub, Inc. via GitHub Security Advisories |
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H (score shown at the top: nvd@nist.gov) Weakness MITRE
Weakness class according to MITRE’s CWE catalog.
Detection
Read off the CVSS vector and the weakness class. Starting points, not tested rules.
- Local/physical vector: focus on endpoint telemetry (EDR) from affected hosts.
- Correlate service crashes/restarts with inbound traffic; repeated crashes may indicate attempts.
Timeline
What happened to this CVE, newest first.
- 2026
- Affected products added · linux/linux
- Record published
- Fix documented
- Affected products added · linux/linux kernel
- CVSS changed · 7.8
- Source status changed · → Modified
- Record created in this database
- 2025
- CVE published
Source activity
Repeated readings are counted rather than listed.
- 2× References added · Oct 14, 2026 – Oct 14, 2026
- 1× Official description updated · Oct 14, 2026 – Oct 14, 2026
References
15 on the record
- git.kernel.org/stable/c/871619c2b78fdfe05afb4e8ba548678687beb812
- git.kernel.org/stable/c/6abb510251e75f875797d8983a830e6731fa281c
- git.kernel.org/stable/c/a4e1ae5c0533964170197e4fb4f33bc8c1db5cd2
- git.kernel.org/stable/c/383d516a0ebc8641372b521c8cb717f0f1834831
- git.kernel.org/stable/c/7828e9363ac4d23b02419bf2a45b9f1d9fb35646
- git.kernel.org/stable/c/90dd2f1b7342b9a671a5ea4160f408037b92b118
- git.kernel.org/stable/c/f64079bef6a8a7823358c3f352ea29a617844636
- git.kernel.org/stable/c/e563b01208f4d1f609bcab13333b6c0e24ce6a01
- lists.debian.org/debian-lts-announce/2025/05/msg00030.html
- github.com/advisories/GHSA-48g3-w2gf-xjrv
- cert-portal.siemens.com/productcert/html/ssa-784472.html
- nvd.nist.gov/vuln/detail/CVE-2025-21704
- lists.debian.org/debian-lts-announce/2025/03/msg00028.html
- project-zero.issues.chromium.org/issues/395107243
- cert-portal.siemens.com/productcert/html/ssa-265688.html
Elsewhere on this site
Related CVEs (same products)
- Critical CVE-2026-99999 ipv4: validate checksum_start before completing checksum 12h
- Unknown CVE-2026-98432 ipv4: free inet_opt and ireq_opt after an RCU grace period 12h
- Unknown CVE-2026-98430 RDMA/efa: Keep admin queues alive while IRQ is registered 1d
- Unknown CVE-2026-98424 wifi: cfg80211: undo netns switch if renaming the wiphy fails 1d
- Unknown CVE-2026-98425 wifi: mac80211: don't warn when an IBSS has no channel to scan 1d
- Unknown CVE-2026-98426 wifi: mwifiex: fix IRQ leak using wrong index in MSI-X error path 1d
Not in any source we poll
Listed rather than left blank: an empty field and an unmeasured one look identical on screen, and only one is a reason to look elsewhere.
- No CISA SSVC assessment.
- No confirmed IOCs, IP addresses, domains, file hashes, or malware artifacts supplied.
- No organization-specific asset inventory, compensating-control status, or patch deployment evidence supplied.
- No exploit packet captures, log samples, or incident case IDs supplied.
Answered from this record
Text assembled only from the fields above — no additional claims.
What should defenders know first?
CVE-2025-21704 is "usb: cdc-acm: Check control transfer buffer size before access", rated High. It affects Linux (Linux); versions are in the scope table. It is not in CISA KEV, which does not rule out exploitation. CVSS 7.8 describes technical severity. EPSS 0.36% estimates the probability of exploitation in 30 days; neither replaces your asset context. First verify whether exposed or business-critical assets run the affected versions, apply vendor fixes or mitigations, and preserve logs for review.
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