---
id: "CVE-2026-121727"
kind: "vulnerability"
aliases: ["CVE-2026-121727"]
title: "Kore: integer underflow in HTTP body handling exhausts server memory"
severity: "high"
cvss: 8.7
epss: null
exploited: false
status: "open"
category: "runtime"
products: []
ecosystems: []
tags: ["c", "http-servers", "kore", "runtime", "self-hosted"]
not_affected_if: ["kore-4.3.0-or-later", "not-using-kore"]
published_at: "2026-11-03T23:17:36+00:00"
first_seen_at: "2026-11-03T23:45:14+00:00"
updated_at: "2026-11-03T23:45:30+00:00"
sources: [{"source": "nvd", "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-121727", "first_seen_at": "2026-11-03T23:45:14+00:00"}]
---

# Kore: integer underflow in HTTP body handling exhausts server memory

Kore is a C web application framework whose HTTP request body handling has an integer underflow that lets unauthenticated clients bypass the http_body_max limit. An attacker can send oversized bodies over many concurrent POST, PUT or DELETE connections and exhaust worker memory.

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

## How to check

- Check the Kore version in use; affected versions are those before `4.3.0`.
- Check whether `http_body_max` is set in the Kore configuration; the sources do not say whether the default configuration is affected.

## Fix

- Kore: upgrade to `4.3.0` or later.

## Timeline

- 2026-11-03T23:45:14+00:00 nvd https://nvd.nist.gov/vuln/detail/CVE-2026-121727

## Documents

- [advisory] Third-party advisory: www.vulncheck.com https://www.vulncheck.com/advisories/kore-before-4.3.0-integer-underflow-memory-exhaustion-via-http-header-recv
- [fix] Patch: github.com https://github.com/jorisvink/kore/commit/1ff3c0f6f7973dc7fc8bf38369790ef2d8079b3b

## From the sources

Kore before 4.3.0 contains an integer underflow vulnerability in HTTP request body handling that allows unauthenticated attackers to bypass http_body_max by sending more body bytes than declared. Attackers can send oversized first segments over many concurrent POST, PUT or DELETE connections, wrapping content_length to grow buffers unbounded and exhaust worker memory.

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