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

Status: published. Published: 2025-12-31. Updated: 2026-11-08.

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).

## Remediation

- fix: The reporting source identifies this reference as a patch. Check the advisory for affected versions and supported release branches. (source: CNA: VulnCheck) — https://github.com/obgm/libcoap/pull/1737
- fix: The reporting source identifies this reference as a patch. Check the advisory for affected versions and supported release branches. (source: CNA: VulnCheck) — https://github.com/obgm/libcoap/commit/30db3ea

## Affected products and versions

- libcoap / libcoap (obgm/libcoap): ≥ 0; ≤ 4.3.5 (affected, semver); 30db3eaa1f0464722ebea2ca2d5084aebfbd344d (unaffected, git). Source: CNA: VulnCheck

## Severity and prioritization

- CVSS 4.0: 8.2 (high); 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; source: CNA: VulnCheck

- CISA KEV: No listing in collected sources

- EPSS: 0.75% as of 2026-11-08; percentile 55.14%

- SSVC: exploitation none; automatable no; technical impact partial; source ADP: CISA-ADP

- Weaknesses: CWE-121

## Exploit evidence

No exploit evidence in collected sources. This is not proof of no exploitation.

## References

- https://github.com/obgm/libcoap/pull/1737 (CNA: VulnCheck; issue-tracking, patch)

- https://github.com/obgm/libcoap/commit/30db3ea (CNA: VulnCheck; patch)

- https://libcoap.net/ (CNA: VulnCheck; product)

- https://www.vulncheck.com/advisories/libcoap-stack-based-buffer-overflow-in-address-resolution-dos-or-potential-rce (CNA: VulnCheck; third-party-advisory)

## Provenance

- CNA: VulnCheck: https://www.cve.org/CVERecord?id=CVE-2025-34468; retrieved 2026-11-08; source updated 2026-11-08

- FIRST EPSS: https://api.first.org/data/v1/epss?cve=CVE-2025-34468; retrieved 2026-11-08; source updated Not reported

Revision: 10538a16c3a3712233e5ee5dde6d089c1eb1e795563a27a6b67fe77ed669c018

Canonical: https://y2.dev/cve/CVE-2025-34468

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