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WorkerdApplication · Cloudflare

CVE-2023-2512

HIGH · 8.1 CVSS v3.1 Published 2023-05-12
Fix available
A fix is available. Upgrade to 1.20230419.0 or later.
See remediation →
90/100
Remediation priority · Urgent
Remotely reachable No privileges Zero-click

Official description Straight from the sourceThe vendor's or NVD's own wording, published unedited. Authoritative, but often terse — it says what broke, rarely what to do.

NVD · unedited
Prior to version v1.20230419.0, the FormData API implementation was subject to an integer overflow. If a FormData instance contained more than 2^31 elements, the forEach() method could end up reading from the wrong location in memory while iterating over elements. This would most likely lead to a segmentation fault, but could theoretically allow arbitrary undefined behavior. In order for the bug to be exploitable, the process would need to be able to allocate 160GB of RAM. Due to this, the bug was never exploitable on the Cloudflare Workers platform, but could theoretically be exploitable on deployments of workerd running on machines with a huge amount of memory. Moreover, in order to be remotely exploited, an attacker would have to upload a single form-encoded HTTP request of at least tens of gigabytes in size. The application code would then have to use request.formData() to parse the request and formData.forEach() to iterate over this data. Due to these limitations, the exploitation likelihood was considered Low. A fix that addresses this vulnerability has been released in version v1.20230419.0 and users are encouraged to update to the latest version available.

Technical summary Written by usOur analysis, written from the advisory, the CVSS vector and the affected-version data. It adds context the advisory leaves out, and never invents facts that are not in the source.

dbcve analysis · high confidence

Integer overflow in FormData API forEach() method in versions prior to v1.20230419.0. When FormData contains more than 2^31 elements, memory reads from incorrect locations during iteration, causing potential segmentation fault or arbitrary undefined behavior.

MitigationUpdate workerd to version v1.20230419.0 or later. Given the high memory requirements (160GB) for exploitation and need for massive HTTP requests, priority should be based on whether your deployment has such memory capacity and accepts large form-encoded requests.

Verify against the referenced sources before acting — the references below are authoritative for this CVE, this summary is not.

Affected products & versions What the vendor confirmedThe version ranges the vendor confirmed as vulnerable. If your version sits inside a range here, treat yourself as exposed until you have upgraded.

NVD · CPE data
WorkerdApplication
Affected:< 1.20230419.0

CVSS breakdown How the score is builtThe industry scoring standard. It rates how the flaw is reached, what it takes to exploit, and what an attacker gains — the score is derived from those, not the other way round.

From the vector
Attack vector
Network
Complexity
High
Privileges
None
User interaction
None
Scope
Unchanged
Confidentiality
High
Integrity
High
Availability
High

CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H

Am I affected? How to checkSteps we derive from the advisory and the affected-version data, so you can decide whether this CVE reaches your setup. They are a guide, not a scan — your own configuration is the authority.

dbcve checks

Work through these to decide whether this CVE applies to you.

  1. Identify workerd installation
    Locate the workerd binary or check if workerd is running as a service. Common locations include /usr/local/bin/workerd or check running processes with 'ps aux | grep workerd'. If using a package manager, query the installed version.
    Affected if workerd is installed and version cannot be determined or is below v1.20230419.0
  2. Determine workerd version
    Run 'workerd --version' or check the version through your deployment tooling (npm, docker image tag, etc.). Compare the version string to v1.20230419.0.
    Affected if Installed version is earlier than v1.20230419.0
  3. Verify FormData API exposure
    Check if your workerd scripts expose any endpoints accepting form-encoded input (application/x-www-form-urlencoded or multipart/form-data). Inspect your worker configuration and script definitions.
    Affected if Endpoints accept FormData submissions and workerd version is vulnerable
  4. Check request size limits
    Review your workerd configuration (*.mjs/js files with runtime config) for any max request size or body parsing limits. Look for settings related to form parsing or body object limits.
    Affected if Request size limits allow large enough payloads to exceed 2^31 FormData elements (requires extremely large submissions)

You are affected if workerd version is earlier than v1.20230419.0 and your service accepts FormData submissions that could exceed 2^31 elements.

Generated from the published advisory. Verify against your own configuration.

Check your environment

Paste your version and any relevant configuration and it will be compared against the affected criteria above. Do not include secrets or credentials.

AI-assisted, checked against the advisory. Informational, not a guarantee.

Remediation Closing itWhat it takes to close this. Where a vendor fix exists we point at it; where none exists we say so plainly, and can build one. Effort estimates are scoped from the advisory, not from your codebase.

dbcve · scoped
Upgrade available Upgrade to 1.20230419.0 or later
Fixed in 1.20230419.0
Interim mitigation

Update workerd to version v1.20230419.0 or later. Given the high memory requirements (160GB) for exploitation and need for massive HTTP requests, priority should be based on whether your deployment has such memory capacity and accepts large form-encoded requests.

Recommended fix High confidence

v1.20230419.0 or later

  1. Identify the current version of workerd in use by checking the deployment or package configuration
  2. Upgrade workerd to version v1.20230419.0 or later (check for the latest available version)
  3. After upgrading, verify that the FormData API works correctly in your application
  4. Ensure your deployment can handle the upgrade without breaking existing functionality

Generated from the published advisory — verify against the referenced sources before acting.

Fix this in Workerd Scoped from the published advisory
  • Consultation2.0 h
  • Implementation1.0 h
  • Testing3.0 h
  • Review / QA2.0 h
8.0 hours of engineering $1,390
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An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $2,224.

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References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.

Primary sources

Practitioner notes

Contributed

Peer-ranked notes from engineers who’ve handled CVE-2023-2512 in production — separate from our analysis above.

No notes yet

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What this is

A place for practitioners to share what actually worked: a mitigation you’ve tested, a configuration change, a version- or environment-specific caveat, or a link to a verified patch. The most useful notes rise to the top as peers upvote them, so the signal stays high.

What belongs here
  • Verified mitigations, workarounds, and config changes
  • Version or environment caveats, and links to real fixes
  • No weaponised exploit code, or anything meant to cause harm
  • No spam, self-promotion, credentials, or personal data