# CVE-2023-6237: Excessive time spent checking invalid RSA public keys

> Attackers can cause denial of service by providing excessively long invalid RSA public keys to applications using OpenSSL's EVP_PKEY_public_check function.

- **Severity:** Medium 5.9 (`CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 25 Apr 2024
- **Updated:** 14 Oct 2026
- **Also known as:** ALPINE-CVE-2023-6237, AZL-39946, AZL-39961, AZL-39968, AZL-42688, AZL-42727, AZL-47670, AZL-78561, BELL-CVE-2023-6237, CLEANSTART-2026-DK63420, CLSA-2025-1741787087, DEBIAN-CVE-2023-6237, GHSA-hvc4-mjv4-5mw6, JLSEC-2026-246, UBUNTU-CVE-2023-6237

## What is CVE-2023-6237?

CVE-2023-6237 is a medium-severity denial of service vulnerability in OpenSSL, published on 25 Apr 2024. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

Issue summary: Checking excessively long invalid RSA public keys may take
a long time.

Impact summary: Applications that use the function EVP_PKEY_public_check()
to check RSA public keys may experience long delays. Where the key that
is being checked has been obtained from an untrusted source this may lead
to a Denial of Service.

When function EVP_PKEY_public_check() is called on RSA public keys,
a computation is done to confirm that the RSA modulus, n, is composite.
For valid RSA keys, n is a product of two or more large primes and this
computation completes quickly. However, if n is an overly large prime,
then this computation would take a long time.

An application that calls EVP_PKEY_public_check() and supplies an RSA key
obtained from an untrusted source could be vulnerable to a Denial of Service
attack.

The function EVP_PKEY_public_check() is not called from other OpenSSL
functions however it is called from the OpenSSL pkey command line
application. For that reason that application is also vulnerable if used
with the '-pubin' and '-check' options on untrusted data.

The OpenSSL SSL/TLS implementation is not affected by this issue.

The OpenSSL 3.0 and 3.1 FIPS providers are affected by this issue.

Weakness: CWE-606 (Unchecked Input for Loop Condition)

## Which versions are affected by CVE-2023-6237?


## How do I fix CVE-2023-6237?

Apply the vendor's patch.

## Is CVE-2023-6237 being exploited?

There is no known exploitation of CVE-2023-6237 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2023-6237 and fix it if it is affected.

What it is: CVE-2023-6237 is a medium-severity denial of service vulnerability in OpenSSL, published on 25 Apr 2024. An attacker can exploit it over the internet without logging in, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2023-6237 in the wild and no public exploit code.

Affected product: OpenSSL. No package-level version data is available, so check the vendor advisory linked from the reference page.

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2023-6237/ (Markdown: https://insights.sbomify.com/CVE-2023-6237/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2023-6237
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2023-6237
- OSV: https://osv.dev/vulnerability/CVE-2023-6237

---
From sbomify Insights: https://insights.sbomify.com/CVE-2023-6237/
Summaries are generated and may contain mistakes; the official description above is the record.