CVE-2025-39682 — Kernel
CRITICALCVE-2025-39682 is a critical-severity (CVSS 9.8) CWE-754 vulnerability in Kernel. 1 public exploit reference exists, so weaponization risk is real. A fix is available for Kernel — see the affected versions and patch details below.
tls: fix handling of zero-length records on the rx_list
Exploitation Status
Actively exploited in the wild
- CISA’s SSVC triage classifies this CVE as under active exploitation.
- CISA assesses this as automatable — exploitation doesn’t require manual, per-target effort, which raises the odds of mass scanning and opportunistic attacks.
- A successful exploit gives an attacker total control of the affected component, not partial access.
Exploitation and automatability from CISA’s SSVC triage for CVE-2025-39682.
EPSS Exploitation Probability
EPSS (Exploit Prediction Scoring System) is a daily probability model maintained by FIRST.org. It estimates the likelihood a CVE will be exploited in production environments within the next 30 days, derived from real-world threat intelligence signals.
How urgent is this, really
CVE-2025-39682 plotted by exploitation likelihood (EPSS) against impact (CVSS). The shaded corner — EPSS 50%+ and CVSS 7.0+ — is where this CVE doesn't sit, though severity or exploitability alone can still warrant action.
Where this sits among everything scored
Of 374,847 CVEs with a current EPSS score, this one falls in the < 10% band (highlighted). Real counts from FIRST.org, not a sample — log-scaled since the landscape is heavily right-skewed.
Real-World Exposure
KernelReal-time download stats are indexed for npm and PyPI packages. This vulnerability affects Linux packages — download data is not available via public APIs for these ecosystems.
Description
In the Linux kernel, the following vulnerability has been resolved:
tls: fix handling of zero-length records on the rx_list
Each recvmsg() call must process either
- only contiguous DATA records (any number of them)
- one non-DATA record
If the next record has different type than what has already been processed we break out of the main processing loop. If the record has already been decrypted (which may be the case for TLS 1.3 where we don't know type until decryption) we queue the pending record to the rx_list. Next recvmsg() will pick it up from there.
Queuing the skb to rx_list after zero-copy decrypt is not possible, since in that case we decrypted directly to the user space buffer, and we don't have an skb to queue (darg.skb points to the ciphertext skb for access to metadata like length).
Only data records are allowed zero-copy, and we break the processing loop after each non-data record. So we should never zero-copy and then find out that the record type has changed. The corner case we missed is when the initial record comes from rx_list, and it's zero length.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 🐧Linux | Kernel | ≥ 6.0.0&&< 6.1.149 | 6.1.149 |
Research use only. For defensive security, authorized penetration testing, and academic research only. Never execute exploit code against systems without explicit written authorization.
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for Kernel, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update Kernel to 6.1.149 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2025-39682 is resolved across your whole dependency graph.
Workarounds
If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.
How O3 protects you
O3 Security's impact-aware SCA analyses which vulnerable code paths your application actually calls, so a match like CVE-2025-39682 can be triaged on real exposure rather than presence alone.
Tailored to CVE-2025-39682. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.
Fixing This On Your OS
If you run this on a Linux distribution, patch through your package manager against the distro's own security advisory below — it tracks the exact backported fix for your release, which can ship on a different timeline (and sometimes a different severity) than the upstream project.
A logic bug in the kTLS receive path mishandles zero-length records taken from the rx_list, allowing a mixed record-type sequence to slip past the per-recvmsg() type constraint and proceed to data processing. The fix initializes and checks the per-call content type (using 0 as “unset”) and bails out when a non-DATA…
| Product | Fixed in | Advisory |
|---|---|---|
| Red Hat Enterprise Linux 10 | kernel-0:6.12.0-55.37.1.el10_0 | RHSA-2025:16904 |
| Red Hat Enterprise Linux 9 | kernel-0:5.14.0-570.49.1.el9_6 | RHSA-2025:16880 |
| Red Hat Enterprise Linux 9.2 Update Services for SAP Solutions | kernel-0:5.14.0-284.144.1.el9_2 | RHSA-2025:19224 |
| Red Hat Enterprise Linux 9.2 Update Services for SAP Solutions | kernel-rt-0:5.14.0-284.144.1.rt14.429.el9_2 | RHSA-2025:19223 |
| Red Hat Enterprise Linux 9.4 Extended Update Support | kernel-0:5.14.0-427.96.1.el9_4 | RHSA-2025:19104 |
Frequently Asked Questions
Is CVE-2025-39682 in your dependencies?
O3 Security finds CVE-2025-39682 across Linux dependencies, including transitive ones, and its impact-aware SCA ranks findings by whether your code actually calls the vulnerable path.