---
id: "CVE-2026-53433"
kind: "vulnerability"
aliases: ["CVE-2026-53433", "GHSA-mvmf-94v6-879g", "GO-2026-6620"]
title: "fzf vulnerable to denial of service through quadratic HTTP request-body accumulation in github.com/junegunn/fzf"
severity: "high"
cvss: 7.5
epss: 0.00378
exploited: false
status: "open"
category: "package"
products: [{"name": "github.com/junegunn/fzf", "fixed": ["0.73.1"], "affected": "< 0.73.1", "ecosystem": "go"}]
ecosystems: ["go"]
tags: ["fzf", "go", "listen-mode", "package"]
not_affected_if: ["fzf 0.73.1 or later", "no --listen flag"]
published_at: "2026-06-30T13:19:13+00:00"
first_seen_at: "2026-10-23T19:13:08+00:00"
updated_at: "2026-10-23T21:45:44+00:00"
sources: [{"source": "govuln", "url": "https://pkg.go.dev/vuln/GO-2026-6620", "first_seen_at": "2026-10-23T19:13:08+00:00"}, {"source": "epss", "url": "https://api.first.org/data/v1/epss?cve=CVE-2026-53433", "first_seen_at": "2026-10-23T19:13:43+00:00"}, {"source": "nvd", "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-53433", "first_seen_at": "2026-10-23T19:35:23+00:00"}]
---

# fzf vulnerable to denial of service through quadratic HTTP request-body accumulation in github.com/junegunn/fzf

fzf's --listen mode parses HTTP POST bodies by repeated string concatenation, which costs quadratic CPU time in the body size. A crafted POST made of many small segments makes one request consume excessive CPU and monopolize the single-threaded server.

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

## Affected

- go:github.com/junegunn/fzf affected < 0.73.1 fixed 0.73.1

## How to check

Run `fzf --version` and check whether it is below 0.73.1.
Search scripts, shell config and FZF_DEFAULT_OPTS for `--listen`.
If --listen is not used, the server is not running.

## Fix

Upgrade fzf to 0.73.1 or later.
If you cannot upgrade right away, stop running fzf with --listen.

## Timeline

- 2026-10-23T19:13:08+00:00 govuln https://pkg.go.dev/vuln/GO-2026-6620
- 2026-10-23T19:13:43+00:00 epss https://api.first.org/data/v1/epss?cve=CVE-2026-53433
- 2026-10-23T19:35:23+00:00 nvd https://nvd.nist.gov/vuln/detail/CVE-2026-53433

## From the sources

fzf is vulnerable to a Denial of Service (DoS) due to inefficient HTTP body processing in the --listen mode due to inefficient HTTP body processing using repeated string concatenation, resulting in quadratic time complexity (O(n²)). A crafted POST request with many small segments can trigger excessive CPU usage during request handling.This allows a single malicious request to monopolize the single‑threaded HTTP server, blocking all other clients and resulting in denial of service.

This issue was fixed in version 0.73.1.

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