# CVE-2026-92391: curl stack overflow in MIME structure cleanup

Source: https://junglewise.ai/threats/cve-2026-92391-a-deeply-nested-multipart-mime-structure-constructed-via-the  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-10-20. Updated: 2026-10-20  
License: CC BY 4.0 with a link back

CVE-2026-92391 · Severity: info · Published 2026-10-20

libcurl is a widely-used library that applications employ to fetch data over the network. When an application using libcurl constructs a deeply nested multipart MIME structure (used for email-like data formatting) through the public API and then cleans it up, the library can crash due to excessive recursion. An attacker who can control MIME structure creation could cause a denial of service affecting any application that uses the vulnerable libcurl.

Technologies: [Curl](https://junglewise.ai/threats/technologies/curl-curl). Vendors: [Curl](https://junglewise.ai/threats/vendors/curl).

## Quick answers

**Is CVE-2026-92391 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-92391 being exploited in the wild.

**How severe is CVE-2026-92391?** Informational severity, published 20 October 2026.

**Which products and versions are affected?** Curl 7.56.0 to 8.22.0 (with fixed branches: 8.14.3, 8.16.2, 8.20.2, 8.23.0+).

**Is there a fix for CVE-2026-92391?** Yes: fixed in curl 8.23.0, 8.20.2 (8.20.x branch), 8.16.2 (8.16.x branch), 8.14.3 (8.14.x branch). Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

**How is CVE-2026-92391 attacked?** It is attacked over the network, in a software library.

**Am I affected by CVE-2026-92391?** Check whether you run Curl at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

## How to fix

- Fixed in curl 8.23.0, 8.20.2 (8.20.x branch), 8.16.2 (8.16.x branch), 8.14.3 (8.14.x branch)

## Technical details

The vulnerability is an uncontrolled recursion issue (CWE-674) in the curl_mime_free function when traversing deeply nested multipart MIME structures. It requires the attacker to construct thousands of nested MIME parts via the libcurl public API and trigger cleanup operations, causing unbounded stack frame allocation that crashes the process. The flaw affects curl 7.56.0 through 8.22.0, with fixes in versions 8.23.0, 8.20.2, 8.16.2, and 8.14.3 for their respective branches.

## Affected products

- curl curl 7.56.0 to 8.22.0 (with fixed branches: 8.14.3, 8.16.2, 8.20.2, 8.23.0+)

## Timeline

- 2026-09-12: disclosed: Issue reported to curl project
- 2026-10-14: patched: curl 8.23.0 released with fix
- 2026-10-14: advisory: Security advisory published

## References

- [https://curl.se/docs/CVE-2026-92391.html](https://curl.se/docs/CVE-2026-92391.html)
- [https://curl.se/docs/CVE-2026-92391.json](https://curl.se/docs/CVE-2026-92391.json)

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