---
id: "CVE-2026-92391"
kind: "vulnerability"
aliases: ["CVE-2026-92391"]
title: "libcurl: deeply nested multipart MIME crashes host process during cleanup"
severity: "unknown"
cvss: null
epss: null
exploited: false
status: "open"
category: "package"
products: []
ecosystems: []
tags: ["c", "c++", "libcurl", "native-code", "package"]
not_affected_if: ["fixed-multipart-only"]
published_at: "2026-10-20T21:17:21+00:00"
first_seen_at: "2026-10-23T21:57:21+00:00"
updated_at: "2026-10-25T05:04:19+00:00"
sources: [{"source": "nvd", "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-92391", "first_seen_at": "2026-10-23T21:57:21+00:00"}]
---

# libcurl: deeply nested multipart MIME crashes host process during cleanup

A deeply nested multipart MIME structure built through libcurl's public API makes curl_mime_free recurse until the stack overflows. The host process crashes, which is a denial of service.

_Summary, check and fix written by a model from the sources; labelled as such._

## How to check

- Check the libcurl version in use with `curl --version` or the library's version API; the sources do not name affected versions.
- Find code that calls `curl_mime_init`, `curl_mime_addpart` or `curl_mime_free` with user-controlled nested multipart data.

## Fix

- Upgrade to a libcurl release that includes the fix; the sources do not name the fixed version, so check the curl project's advisory for CVE-2026-92391.
- Until patched, limit or reject user-supplied multipart nesting depth before building the MIME structure.

## Timeline

- 2026-10-23T21:57:21+00:00 nvd https://nvd.nist.gov/vuln/detail/CVE-2026-92391

## From the sources

A deeply nested multipart MIME structure constructed via the public API causes
a stack overflow in libcurl during normal cleanup operations. An excessive
recursion depth within `curl_mime_free` leads to unbounded stack frame
allocation during structure traversal, ultimately crashing the host process.

---

_Free to read at a human pace. An API with keys and an MCP server are in preparation; early access: hello@infrastack.ai_