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LibcoapApplication

CVE-2025-34468

CRITICAL · 9.8 CVSS v3.1 Published 2025-12-31
Fix available
A fix is available. Upgrade to after 4.3.5 or later.
See remediation →
100/100
Remediation priority · Urgent
Remotely reachable No privileges Zero-click Patch available

Official description Straight from the sourceThe vendor's or NVD's own wording, published unedited. Authoritative, but often terse — it says what broke, rarely what to do.

NVD · unedited
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).

Technical summary Written by usOur analysis, written from the advisory, the CVSS vector and the affected-version data. It adds context the advisory leaves out, and never invents facts that are not in the source.

dbcve analysis · high confidence

Stack-based buffer overflow in libcoap's address resolution where attacker-controlled hostname data is copied into a fixed 256-byte stack buffer without bounds checking. Exploitation requires the proxy logic to be enabled, allowing a remote attacker to potentially achieve RCE.

MitigationUpdate libcoap to version 4.3.6 or later (post commit 30db3ea) which contains proper bounds checking. If patching is not immediately possible, disable proxy functionality until the update can be applied.

Verify against the referenced sources before acting — the references below are authoritative for this CVE, this summary is not.

Affected products & versions What the vendor confirmedThe version ranges the vendor confirmed as vulnerable. If your version sits inside a range here, treat yourself as exposed until you have upgraded.

NVD · CPE data
LibcoapApplication
Affected:<= 4.3.5

CVSS breakdown How the score is builtThe industry scoring standard. It rates how the flaw is reached, what it takes to exploit, and what an attacker gains — the score is derived from those, not the other way round.

From the vector
Attack vector
Network
Complexity
Low
Privileges
None
User interaction
None
Scope
Unchanged
Confidentiality
High
Integrity
High
Availability
High

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

Am I affected? How to checkSteps we derive from the advisory and the affected-version data, so you can decide whether this CVE reaches your setup. They are a guide, not a scan — your own configuration is the authority.

dbcve checks

Work through these to decide whether this CVE applies to you.

  1. Identify libcoap version
    Run `coap-client --version` or check package manager output (`dpkg -l libcoap*`, `rpm -qa | grep libcoap`, or `brew list libcoap`). If compiled from source, check the version string in source files or the library filename.
    Affected if version is 4.3.5 or earlier (including any 4.x.x version up to 4.3.5)
  2. Determine if proxy functionality is enabled
    Search application configuration files or runtime settings for coap-proxy features. If using a libcoap-based application, review its startup logs or configuration for proxy-related options (such as `proxy` directive, port 5684/5685 proxy ports, or proxy URI parameters).
    Affected if proxy logic is enabled or configurable in the deployment

You are affected if libcoap version is 4.3.5 or earlier AND proxy functionality is enabled in your application or service.

Generated from the published advisory. Verify against your own configuration.

Check your environment

Paste your version and any relevant configuration and it will be compared against the affected criteria above. Do not include secrets or credentials.

AI-assisted, checked against the advisory. Informational, not a guarantee.

Remediation Closing itWhat it takes to close this. Where a vendor fix exists we point at it; where none exists we say so plainly, and can build one. Effort estimates are scoped from the advisory, not from your codebase.

dbcve · scoped
Upgrade available Upgrade to a release after 4.3.5
Vendor patch github.com →
Interim mitigation

Update libcoap to version 4.3.6 or later (post commit 30db3ea) which contains proper bounds checking. If patching is not immediately possible, disable proxy functionality until the update can be applied.

Recommended fix Moderate confidence

libcoap 4.3.6 or later (commit 30db3ea and beyond)

  1. 1. Identify all applications and systems using libcoap with proxy functionality enabled
  2. 2. Locate the libcoap library installation (check build systems, package dependencies, or embedded copies)
  3. 3. Download or obtain libcoap source code from the official repository: https://github.com/obgm/libcoap
  4. 4. Verify the fix by checking out or downloading code after commit 30db3ea (or version 4.3.6 and later if available)
  5. 5. Rebuild the library with the fixed code: ./configure && make
  6. 6. Replace the vulnerable libcoap library in all affected applications
  7. 7. Rebuild and redeploy all applications that link against libcoap
  8. 8. Verify the proxy functionality still works correctly after the update
Caveat Minimal expected; the fix adds bounds checking without changing API behavior. However, test thoroughly as with any library upgrade.

Generated from the published advisory — verify against the referenced sources before acting.

Fix this in Libcoap Scoped from the published advisory
  • Consultation2.0 h
  • Implementation4.0 h
  • Testing8.0 h
  • Review / QA3.0 h
17.0 hours of engineering $2,860
Get the upgrade done

An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $4,576.

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References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.

Primary sources

Practitioner notes

Contributed

Peer-ranked notes from engineers who’ve handled CVE-2025-34468 in production — separate from our analysis above.

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What this is

A place for practitioners to share what actually worked: a mitigation you’ve tested, a configuration change, a version- or environment-specific caveat, or a link to a verified patch. The most useful notes rise to the top as peers upvote them, so the signal stays high.

What belongs here
  • Verified mitigations, workarounds, and config changes
  • Version or environment caveats, and links to real fixes
  • No weaponised exploit code, or anything meant to cause harm
  • No spam, self-promotion, credentials, or personal data