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WolfsslApplication

CVE-2026-3549

CRITICAL · 9.8 CVSS v3.1 Published 2026-03-19
Fix available
A fix is available. Upgrade to 5.9.0 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
Heap Overflow in TLS 1.3 ECH parsing. An integer underflow existed in ECH extension parsing logic when calculating a buffer length, which resulted in writing beyond the bounds of an allocated buffer. Note that in wolfSSL, ECH is off by default, and the ECH standard is still evolving.

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 · moderate confidence

A heap overflow vulnerability exists in wolfSSL's TLS 1.3 ECH (Encrypted Client Hello) extension parsing due to an integer underflow when calculating buffer lengths. This causes writes beyond allocated buffer bounds. ECH is off by default in wolfSSL.

MitigationEnsure ECH remains disabled until a patch is applied; monitor for wolfSSL security updates addressing this integer underflow in ECH parsing logic.

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 version
    Run 'wolfssl version' or check the library file version. If using a package manager, run 'dpkg -l libwolfssl' (Debian) or 'rpm -qi wolfssl' (RHEL). Alternatively, check the header file version.h or the library symlink.
    Affected if The installed version is less than 5.9.0
  2. Confirm TLS 1.3 support
    Review wolfSSL build configuration for TLS 1.3 enablement. Check for '--enable-tls13' or 'HAVE_TLS13' in build flags. Inspect /usr/local/include/wolfssl/options.h or similar options file if installed.
    Affected if TLS 1.3 support is compiled into the library
  3. Check if ECH is enabled
    Inspect wolfSSL configuration for ECH. Look for '--enable-ech' or 'WOLFSSL_HAVE_ECH' in build options. On Linux, check /etc/wolfssl/options or the compiled configuration file. If using a custom build, review the ./configure or CMake flags used.
    Affected if ECH (Encrypted Client Hello) is explicitly enabled in the build configuration

You are affected if wolfSSL version is below 5.9.0 AND ECH is enabled AND TLS 1.3 support is compiled in, since the heap overflow only occurs during TLS 1.3 ECH extension parsing with ECH turned on.

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 5.9.0 or later
Fixed in 5.9.0
Vendor patch github.com →
Interim mitigation

Ensure ECH remains disabled until a patch is applied; monitor for wolfSSL security updates addressing this integer underflow in ECH parsing logic.

Recommended fix High confidence

5.9.0

  1. 1. Identify the current WolfSSL version in use by checking your project dependencies or running `wolfssl -version`
  2. 2. Stop any services or applications using WolfSSL to prevent potential exploitation during upgrade
  3. 3. Upgrade WolfSSL to version 5.9.0 or later. For example, using git: `git clone https://github.com/wolfSSL/wolfssl.git && cd wolfssl && git checkout v5.9.0`
  4. 4. Rebuild and reinstall the library: `./autogen.sh && ./configure && make && make install`
  5. 5. Update any dependent applications to link against the new library version
  6. 6. Restart services that use WolfSSL
  7. 7. Verify the upgrade was successful by checking the version again
Caveat wolfSSL 5.9.0 includes the fix; the ECH standard is evolving so ensure compatibility if ECH is enabled

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

Fix this in Wolfssl Scoped from the published advisory
  • Consultation3.0 h
  • Implementation6.0 h
  • Testing5.0 h
  • Review / QA3.0 h
17.0 hours of engineering $2,970
Get the upgrade done

An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $4,752.

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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-2026-3549 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
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