CVE-2023-2512

Buffer under-read in workerd

References

Release - https://github.com/cloudflare/workerd/releases/tag/v1.20230419.0

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 read operation accesses a memory location beyond the intended buffer boundary. Typical impact: sensitive data disclosure or crash.

CVE-2023-2512 has a CVSS score of 6.5 (Medium). The vector is network-reachable, no privileges required, and no user interaction. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment. A fixed version is available (1.20230419.0); upgrading removes the vulnerable code path.

Kodem intelligence

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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.

1. What is CVE-2023-2512? CVE-2023-2512 is a medium-severity out-of-bounds read vulnerability in workerd (npm), affecting versions < 1.20230419.0. It is fixed in 1.20230419.0. A read operation accesses a memory location beyond the intended buffer boundary.
2. How severe is CVE-2023-2512? CVE-2023-2512 has a CVSS score of 6.5 (Medium). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
3. Which versions of workerd are affected by CVE-2023-2512? workerd (npm) versions < 1.20230419.0 is affected.
4. Is there a fix for CVE-2023-2512? Yes. CVE-2023-2512 is fixed in 1.20230419.0. Upgrade to this version or later.
5. Is CVE-2023-2512 exploitable, and should I be worried? Whether CVE-2023-2512 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
6. What actually determines whether CVE-2023-2512 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
7. How do I fix CVE-2023-2512? Upgrade workerd to 1.20230419.0 or later.