---
id: "CVE-2026-92387"
kind: "vulnerability"
aliases: ["CVE-2026-92387"]
title: "curl: malicious FTP, IMAP, POP3 or SMTP server blocks transfers indefinitely"
severity: "medium"
cvss: null
epss: null
exploited: false
status: "open"
category: "package"
products: []
ecosystems: []
tags: ["c", "libcurl", "package", "php", "python", "self-hosted"]
not_affected_if: ["http-only", "trusted-servers-only"]
published_at: "2026-10-20T21:17:21+00:00"
first_seen_at: "2026-10-23T21:57:21+00:00"
updated_at: "2026-10-25T05:04:23+00:00"
sources: [{"source": "nvd", "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-92387", "first_seen_at": "2026-10-23T21:57:21+00:00"}]
---

# curl: malicious FTP, IMAP, POP3 or SMTP server blocks transfers indefinitely

A malicious FTP, IMAP, POP3 or SMTP server can omit the final control-response line so libcurl never finishes the exchange. This bypasses the configured transfer timeout and blocks all other transfers sharing the same multi-handle indefinitely.

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

## How to check

- Run `curl --version` and note the libcurl version listed on the second line
- Check whether your application uses libcurl's multi interface (curl_multi_*) with FTP, IMAP, POP3 or SMTP URLs
- unknown

## Fix

- Upgrade libcurl to a fixed release; the sources do not name the fixed version, so check the curl project advisory
- Until patched, avoid connecting to untrusted FTP, IMAP, POP3 or SMTP servers through a shared multi-handle
- unknown

## Timeline

- 2026-10-23T21:57:21+00:00 nvd https://nvd.nist.gov/vuln/detail/CVE-2026-92387

## From the sources

By permanently omitting the final control-response line, a malicious FTP,
IMAP, POP3, or SMTP server can exploit libcurl and completely bypass its
configured transfer timeout mechanism, indefinitely blocking all concurrent
transfers bound to the same multi-handle.

---

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