---
id: "CVE-2026-92389"
kind: "vulnerability"
aliases: ["CVE-2026-92389"]
title: "libcurl: TFTP state flaw can leak POST upload data to malicious servers"
severity: "unknown"
cvss: null
epss: null
exploited: false
status: "open"
category: "runtime"
products: []
ecosystems: []
tags: ["c", "libcurl", "runtime", "self-hosted", "tftp"]
not_affected_if: ["no-handle-reuse", "no-tftp-use"]
published_at: "2026-10-20T21:17:21+00:00"
first_seen_at: "2026-10-23T21:57:21+00:00"
updated_at: "2026-10-25T05:04:21+00:00"
sources: [{"source": "nvd", "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-92389", "first_seen_at": "2026-10-23T21:57:21+00:00"}]
---

# libcurl: TFTP state flaw can leak POST upload data to malicious servers

libcurl does not check that a TFTP server's replies match the requested transfer direction, so a malicious TFTP server can make a download request trigger an upload. The client then sends data from the handle's persistent CURLOPT_READDATA buffer, which can include leftover data from an earlier HTTP POST on a reused handle.

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

## How to check

- Run `curl --version` and compare the libcurl version against the fixed release (unknown in the sources)
- Check whether application code uses TFTP URLs (`tftp://`) with libcurl
- Check whether handles are reused across requests with CURLOPT_READDATA set

## Fix

- Upgrade libcurl to a patched release (fixed version unknown in the sources)
- Avoid fetching `tftp://` URLs from untrusted servers until patched
- Do not reuse a handle across unrelated uploads and downloads

## Timeline

- 2026-10-23T21:57:21+00:00 nvd https://nvd.nist.gov/vuln/detail/CVE-2026-92389

## From the sources

libcurl's TFTP state machine fails to validate state transitions against the
requested transfer direction, accepting opening server responses for both
reads and writes interchangeably. A malicious TFTP server can respond to a
download request in a way that forces the client into transmit mode, prompting
libcurl to consume and transmit data from the handle's persistent
`CURLOPT_READDATA` pointer - including data remaining from unrelated prior
operations, such as an HTTP POST request executed on a reused handle.

---

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