# CVE-2023-27537: Use after free in https://github.com/curl/curl

> A double free or use-after-free in libcurl's HSTS sharing allows attackers to cause crashes or execute code when multiple threads share data.

- **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:** 30 Mar 2023
- **Updated:** 14 Oct 2026
- **Also known as:** ALPINE-CVE-2023-27537, AZL-25852, AZL-25858, AZL-34603, AZL-38114, CLEANSTART-2026-NT49097, CURL-CVE-2023-27537, DEBIAN-CVE-2023-27537, GHSA-9j2c-vm53-wcvm, JLSEC-2025-32

## What is CVE-2023-27537?

CVE-2023-27537 is a medium-severity use after free vulnerability in Haxx Libcurl, published on 30 Mar 2023. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

A double free vulnerability exists in libcurl <8.0.0 when sharing HSTS data between separate "handles". This sharing was introduced without considerations for do this sharing across separate threads but there was no indication of this fact in the documentation. Due to missing mutexes or thread locks, two threads sharing the same HSTS data could end up doing a double-free or use-after-free.

Weakness: CWE-415 (Double Free)

## Which versions are affected by CVE-2023-27537?

It affects 9 products.


Products: Broadcom Brocade Fabric Operating System Firmware, Haxx Libcurl, Netapp Active Iq Unified Manager, Netapp Clustered Data Ontap, Netapp H300s Firmware, Netapp H410s Firmware, Netapp H500s Firmware, Netapp H700s Firmware, Splunk Universal Forwarder.

## How do I fix CVE-2023-27537?

Upgrade to a fixed version.

## Is CVE-2023-27537 being exploited?

There is no known exploitation of CVE-2023-27537 in the wild and no public exploit code.

## Other vulnerabilities in Haxx Libcurl

- [CVE-2023-27534](https://insights.sbomify.com/CVE-2023-27534/): Path traversal in https://github.com/curl/curl (high 8.8)
- [CVE-2021-4197](https://insights.sbomify.com/CVE-2021-4197/): Privilege escalation in kernel (high 7.8)
- [CVE-2023-27538](https://insights.sbomify.com/CVE-2023-27538/): Auth bypass in https://github.com/curl/curl (high 7.7)
- [CVE-2021-27218](https://insights.sbomify.com/CVE-2021-27218/): Integer overflow in n/a (high 7.5)
- [CVE-2021-27219](https://insights.sbomify.com/CVE-2021-27219/): Integer overflow in n/a (high 7.5)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2023-27537 and fix it if it is affected.

What it is: CVE-2023-27537 is a medium-severity use after free vulnerability in Haxx Libcurl, published on 30 Mar 2023. 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-2023-27537 in the wild and no public exploit code.

Affected product: Haxx Libcurl. 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-2023-27537/ (Markdown: https://insights.sbomify.com/CVE-2023-27537/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2023-27537
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2023-27537
- OSV: https://osv.dev/vulnerability/CVE-2023-27537

---
From sbomify Insights: https://insights.sbomify.com/CVE-2023-27537/
Summaries are generated and may contain mistakes; the official description above is the record.