---
id: CVE-2025-34468
title: >-
  libcoap versions up to and including 4.3.5, prior to commit 30db3ea, contain a
  stack-based buffer overflow in address resolution when attacker-controlled
  hostname data is copied into a fixed 256-byte stack buffer without proper
  bounds ch…
summary: >-
  libcoap versions up to and including 4.3.5, prior to commit 30db3ea, contain a
  stack-based buffer overflow in address resolution when attacker-controlled
  hostname data is copied into a fixed 256-byte stack buffer without proper
  bounds ch…
severity: critical
cvss: 9.8
cvssVector: 'CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H'
cwe:
  - CWE-121
  - CWE-787
vendor: libcoap
product: libcoap
affected:
  - libcoap <= 4.3.5
published: '2025-12-31'
updated: '2026-09-23'
sourceUpdated: '2026-09-23T14:10:00.190'
source: NVD
sourceUrl: 'https://nvd.nist.gov/vuln/detail/CVE-2025-34468'
references:
  - url: 'https://github.com/obgm/libcoap/commit/30db3ea'
    label: disclosure@vulncheck.com
  - url: 'https://github.com/obgm/libcoap/pull/1737'
    label: disclosure@vulncheck.com
  - url: 'https://libcoap.net/'
    label: disclosure@vulncheck.com
  - url: >-
      https://www.vulncheck.com/advisories/libcoap-stack-based-buffer-overflow-in-address-resolution-dos-or-potential-rce
    label: disclosure@vulncheck.com
tags:
  - nvd
epss: 0.00748
epssPercentile: 0.53019
ingestedAt: '2026-07-15T13:44:03.666Z'
---

## Overview

libcoap versions up to and including 4.3.5, prior to commit 30db3ea, contain a stack-based buffer overflow in address resolution when attacker-controlled hostname data is copied into a fixed 256-byte stack buffer without proper bounds checking. A remote attacker can trigger a crash and potentially achieve remote code execution depending on compiler options and runtime memory protections. Exploitation requires the proxy logic to be enabled (i.e., the proxy request handling code path in an application using libcoap).

## Affected

- `libcoap <= 4.3.5`

## Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.