dbcve.org
WolfsslApplication

CVE-2026-5187

CRITICAL · 9.8 CVSS v3.1 Published 2026-04-09
Fix available
A fix is available. Upgrade to after 5.9.0 or later.
See remediation →
100/100
Remediation priority · Urgent
Remotely reachable No privileges Zero-click

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
Two potential heap out-of-bounds write locations existed in DecodeObjectId() in wolfcrypt/src/asn.c. First, a bounds check only validates one available slot before writing two OID arc values (out[0] and out[1]), enabling a 2-byte out-of-bounds write when outSz equals 1. Second, multiple callers pass sizeof(decOid) (64 bytes on 64-bit platforms) instead of the element count MAX_OID_SZ (32), causing the function to accept crafted OIDs with 33 or more arcs that write past the end of the allocated buffer.

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

Heap out-of-bounds write vulnerability in wolfcrypt's DecodeObjectId() function in wolfcrypt/src/asn.c. The first issue allows a 2-byte out-of-bounds write when outSz equals 1 because a bounds check validates only one slot before writing two OID arc values (out[0] and out[1]). The second issue occurs when callers pass sizeof(decOid) (64 bytes on 64-bit) instead of MAX_OID_SZ (32 elements), enabling crafted OIDs with 33+ arcs to write past the allocated buffer end.

MitigationFix the bounds check to validate both slots before writing out[0] and out[1], and update all callers to pass the correct element count MAX_OID_SZ (32) rather than sizeof(decOid). Update to a patched version of wolfcrypt.

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
WolfsslApplication
Affected:<= 5.9.0

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 wolfssl installation and version
    Run 'wolfssl version' or check package manager (dpkg -l | grep wolfssl, rpm -qa | grep wolfssl) to determine if wolfssl is installed and its version number
    Affected if Installed version is 5.9.0 or lower
  2. Locate the vulnerable asn.c source file
    Check if wolfcrypt/src/asn.c exists in the installation (typically in /usr/include/wolfssl/wolfcrypt/ or the source tree). If compiling from source, locate the asn.c file and inspect the DecodeObjectId() function for the bounds check logic
    Affected if The DecodeObjectId() function is present and the outSz bounds check only validates one slot before writing out[0] and out[1]
  3. Determine if OID decoding is in use
    Inspect application code or configuration for calls to DecodeObjectId, or look for ASN.1 OID parsing functionality (search for 'OID' or 'objectId' in codebase and configuration). Check if asn.c is compiled into the wolfcrypt library
    Affected if Applications parse ASN.1 Object Identifiers using the vulnerable DecodeObjectId function
  4. Check buffer size parameter passed to DecodeObjectId callers
    Review all call sites to DecodeObjectId in the codebase and verify whether callers pass sizeof(decOid) instead of MAX_OID_SZ (32). Search for 'sizeof(decOid)' near DecodeObjectId calls
    Affected if Callers pass sizeof(decOid) (64 bytes on 64-bit) rather than MAX_OID_SZ (32 elements) as the buffer size parameter

The environment is affected if wolfssl version is 5.9.0 or lower and the DecodeObjectId function with OID parsing is actively used, with callers potentially passing incorrect buffer sizes.

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 5.9.0
Interim mitigation

Fix the bounds check to validate both slots before writing out[0] and out[1], and update all callers to pass the correct element count MAX_OID_SZ (32) rather than sizeof(decOid). Update to a patched version of wolfcrypt.

Recommended fix Moderate confidence

WolfSSL 5.9.1 or later

  1. 1. Identify all applications and services that use the WolfSSL library in your environment.
  2. 2. Locate the WolfSSL library version currently deployed (check library files or build system for version string).
  3. 3. Download or obtain WolfSSL version 5.9.1 or later from the official WolfSSL repository at https://github.com/wolfSSL/wolfssl.
  4. 4. Review the release notes for version 5.9.1 to confirm the CVE-2026-5187 fix is included.
  5. 5. Rebuild or replace the WolfSSL library in your application stack with the updated version.
  6. 6. Test your application functionality to ensure compatibility with the updated library.
  7. 7. Redeploy the updated application to all production environments.
Caveat Review release notes for any API changes or compatibility notes between 5.9.0 and the target upgrade version before deploying

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

Fix this in Wolfssl Scoped from the published advisory
  • Consultation4.0 h
  • Implementation8.0 h
  • Testing12.0 h
  • Review / QA4.0 h
28.0 hours of engineering $4,760
Get the upgrade done

An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $7,616.

Scan for this in your stack

Free · runs locally
dbcve dependency scanner

Check whether your project pulls in CVE-2026-5187 — or any other known-vulnerable package — straight from your lock files. Free and open source; it runs locally and uploads nothing.

Get it on GitHub Scan in the browser

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-2026-5187 in production — separate from our analysis above.

No notes yet

Be the first to add a field note for this CVE — a mitigation you’ve verified, a version caveat, or a link to a working fix. Sign in above to contribute.

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