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Linux Kernel Use-After-Free Vulnerability

Known exploitedExploited · KEV 2023-03-30CVE-2023-0266CWE-416

Exploited since 2023-03-30. No WAF vendor names it yet.

Edge rules
0/8
Our test
No exploit yet
CVSS
7.9
EPSS
3.7% Top 10%
Posts, 14d
02026-10-22: 0 posts2026-10-23: 0 posts2026-10-24: 0 posts2026-10-25: 0 posts2026-10-26: 0 posts2026-10-27: 0 posts2026-10-28: 0 posts2026-10-29: 0 posts2026-10-30: 0 posts2026-10-31: 0 posts2026-11-01: 0 posts2026-11-02: 0 posts2026-11-03: 0 posts2026-11-04: 0 posts
Published
2023-01-30
A use after free vulnerability exists in the ALSA PCM package in the Linux Kernel. SNDRV_CTL_IOCTL_ELEM_{READ|WRITE}32 is missing locks that can be used in a use-after-free that can result in a priviledge escalation to gain ring0 access… More

A use after free vulnerability exists in the ALSA PCM package in the Linux Kernel. SNDRV_CTL_IOCTL_ELEM_{READ|WRITE}32 is missing locks that can be used in a use-after-free that can result in a priviledge escalation to gain ring0 access from the system user. We recommend upgrading past commit 56b88b50565cd8b946a2d00b0c83927b7ebb055e

Known exploitedLast checked 2026-11-04

The risk

CISA lists CVE-2023-0266 as exploited in the wild since 2023-03-30. No edge WAF vendor names it in a changelog, so default managed rules may or may not catch it.

Who is affected

Teams running Linux Kernel. Affected versions are in the vendor advisory.

Next steps

  1. Find the version you run. On the host:
    uname -r
  2. Apply the vendor's fix; the advisory lists the affected and fixed versions. git.kernel.org ↗
  3. CISA's required action: Apply updates per vendor instructions. US federal agencies must act by 2023-04-20.
  4. Review exposed instances for signs of compromise: it was exploited before many systems were patched, and a later patch does not undo access already gained.
  5. Do not rely on WAF defaults: no edge vendor names this CVE. Restrict access to the vulnerable component or add a custom rule until it is patched. Edge coverage
  6. Check which WAF sits in front of your site and whether it covers this CVE. Check your domain

Attack traffic on Cloudflare

Cloudflare Radar
  • Rules for named CVEs5.9% of mitigated layer 7 attacks, 7 days2026-10-06: 0.6%2026-10-07: 1.8%2026-10-08: 3%2026-10-09: 6.3%2026-10-10: 1.9%2026-10-11: 0.8%2026-10-12: 0.6%2026-10-13: 0.6%2026-10-14: 4.2%2026-10-15: 2.3%2026-10-16: 1.3%2026-10-17: 1.6%2026-10-18: 1.1%2026-10-19: 3.2%2026-10-20: 4.7%2026-10-21: 5.7%2026-10-22: 5.5%2026-10-23: 9.8%2026-10-24: 7%2026-10-25: 5%2026-10-26: 7.3%2026-10-27: 8.1%2026-10-28: 10.1%2026-10-29: 0.9%2026-10-30: 4.1%2026-10-31: 7.5%2026-11-01: 8.7%2026-11-02: 2.4%2026-11-03: 9.1%

Radar groups Cloudflare's WAF managed rules by category; it does not publish counts per CVE. These shares show how much attack traffic targets this kind of flaw across Cloudflare's network (28-day trend). They are not compromised systems, and seeing few attempts on Cloudflare does not prove an absence elsewhere. Radar data as of 2026-11-03. Radar ↗

Check your exposure with an agent

Read-only

Copy this into an agent with access to your infrastructure. It asks for an evidence-based, read-only assessment: affected systems, exposure, compensating controls and what is still unknown. It does not scan or change anything by itself.

Prompt12 lines
Assess whether the infrastructure available to you is affected by CVE-2023-0266 (Linux Kernel Use-After-Free Vulnerability). Perform a read-only assessment within your authorized access. Do not send exploit traffic, scan third-party systems, change configuration or restart services.

1. Verify the CVE record at https://www.cve.org/CVERecord?id=CVE-2023-0266 and the vendor advisory. Establish affected and fixed versions, including vendor backports. Cite sources and retrieval dates; flag anything you cannot verify.
2. Inventory deployments of Linux Kernel: asset, environment, owner where known, installed version or build, and how you confirmed it (package metadata, a version endpoint, image tags), e.g. `uname -r` (on the host). An image tag alone does not prove the running version.
3. Identify which deployments are reachable from the internet or untrusted networks, and through which paths (direct origin, load balancer, CDN or WAF).
4. Assess compensating controls separately from patch status. Current edge WAF coverage for this CVE: no edge WAF vendor names it. Live data: https://cve.vigilbase.com/api/v1/cves/CVE-2023-0266. Check whether the rule is enabled and in block mode on each path, and whether any path bypasses the WAF. A WAF rule is not a patch.
5. It is known exploited (CISA KEV): review logs on exposed instances for signs of exploitation before and after patching.

Return a short summary and a table: asset | version/build | assessment (affected, fixed, not applicable, unknown) | exposure | compensating control | evidence | next action. List what you could not assess and the access needed to resolve it. Do not infer absence of compromise from patch status or a lack of alerts.

Remediation guidance: Apply the vendor's fix; the advisory lists the affected and fixed versions. CISA's required action: Apply updates per vendor instructions. US federal agencies must act by 2023-04-20.
More: https://cve.vigilbase.com/cve/CVE-2023-0266

Sources

Cited
CVE record

CVSS 3.1 7.9 (high). Weakness: CWE-416.

CVE-2023-0266 ↗NVD ↗

Vendor advisory

Fixes and mitigations the CVE record links to. Check affected builds against the vendor, including backports.

git.kernel.org ↗

Exploit evidence

No public exploit code found in Exploit-DB, Metasploit, nuclei-templates or GitHub. That does not mean none exists.

CISA KEV

Added 2023-03-30, federal due date 2023-04-20 (catalog 2026.11.03, checked 2026-11-04).

CISA KEV catalog ↗

EPSS

3.70% probability of exploitation activity in the next 30 days, higher than 89% of CVEs (2026-11-02).

FIRST EPSS ↗

WAF vendor statements

No edge vendor changelog names it.

Ask Vigil

AI · answers from this page
Ask about CVE-2023-0266: who's covered, what to patch first, how vendors compare. I cite sources and won't help with attacks.

Severity, decoded

CVSS 3.1
High · 7.9 / 10

Exploitable from an adjacent network under specific conditions, with low privileges and no user interaction, leading to low impact on confidentiality and full loss of integrity and availability, and the impact can reach components beyond the vulnerable one.

Same network onlyAny user loginNo user actionHard to pull offSpreads beyond the appSerious impact
How the score is built8 metrics
  • Attack vectorAn attacker must be on the same local network, Wi-Fi or VPN segment.
    Adjacent network
  • Attack complexityThe attack only works when conditions outside the attacker's control line up.
    High
  • Privileges requiredThe attacker needs an ordinary user account.
    Low
  • User interactionNo one has to click or open anything; the attack works on its own.
    None
  • ScopeThe attack can spread beyond the vulnerable component to other parts of the system.
    Changed
  • Confidentiality impactAn attacker can read some data, but has no control over what they get.
    Low
  • Integrity impactAn attacker can change any data or files the affected component protects.
    High
  • Availability impactAn attacker can take the component down completely or keep it from serving anyone.
    High
CVSS:3.1/AV:A/AC:H/PR:L/UI:N/S:C/C:L/I:H/A:H
CISA's assessmentSSVC, from the CVE record
ExploitationActive

Attackers are exploiting this in the wild.

AutomatableNo

At least one step needs hands-on work, which slows mass attacks.

Technical impactTotal

A successful attack gives full control over the affected software or all of its data.

Public exploits

None found
0 Metasploit0 Exploit-DB0 Scanner template0 GitHub PoCs

No exploit in Exploit-DB or Metasploit, and no scanner template. That lowers, but doesn't remove, the chance of mass exploitation.

Timeline

  1. 2023-01-30
    CVE published
    CVE List
  2. 2023-03-30
    Added to CISA KEV
    Confirmed exploitation in the wild

Social

2026-10-22: 0 posts2026-10-23: 0 posts2026-10-24: 0 posts2026-10-25: 0 posts2026-10-26: 0 posts2026-10-27: 0 posts2026-10-28: 0 posts2026-10-29: 0 posts2026-10-30: 0 posts2026-10-31: 0 posts2026-11-01: 0 posts2026-11-02: 0 posts2026-11-03: 0 posts2026-11-04: 0 posts

No posts seen yet on X, Bluesky, Mastodon, Hacker News or GitHub.

Vendor statements

Quoted
CloudflareWAF Managed RulesBefore feed history

The CVE predates the oldest entry in this vendor's public feed, so a rule may exist that we cannot see.

AWSAWS WAF Managed RulesNo public claim

We found no public statement from this vendor naming this CVE. That is not proof of no protection: generic rules may still catch it. AWS often describes a vulnerability without naming its CVE (for example "Log4j"). We count only entries that name the CVE, so AWS coverage is understated.

Microsoft AzureFront Door and Application Gateway WAF (DRS)No public claim

We found no public statement from this vendor naming this CVE. That is not proof of no protection: generic rules may still catch it. The rule tables name CVEs but carry no dates, so Azure is left out of every time-to-rule figure.

Google CloudCloud Armor preconfigured WAF rulesBefore feed history

The CVE predates the oldest entry in this vendor's public feed, so a rule may exist that we cannot see.

FastlyNext-Gen WAF virtual patchesBefore feed history

The CVE predates the oldest entry in this vendor's public feed, so a rule may exist that we cannot see.

F5Attack signatures (Distributed Cloud WAF)No public claim

We found no public statement from this vendor naming this CVE. That is not proof of no protection: generic rules may still catch it. Each signature lists the CVEs it references, with its id and date. F5 does not state a default action; signatures enforce once staging ends in your policy.

AkamaiApp & API Protector (Adaptive Security Engine)No public source

This vendor publishes no machine-readable rule changelog we can check.

OWASP CRSCore Rule Set (open source, used inside many WAFs)No public claim

We found no public statement from this vendor naming this CVE. That is not proof of no protection: generic rules may still catch it. CRS rarely names CVEs: it relies on generic detections. Our own lab measures what it actually blocks.