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WolfsslApplication

CVE-2026-3849

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
Stack Buffer Overflow in wc_HpkeLabeledExtract via Oversized ECH Config. A vulnerability existed in wolfSSL 5.8.4 ECH (Encrypted Client Hello) support, where a maliciously crafted ECH config could cause a stack buffer overflow on the client side, leading to potential remote execution and client program crash. This could be exploited by a malicious TLS server supporting ECH. Note that ECH is off by default, and is only enabled with enable-ech.

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 buffer overflow in wolfSSL's wc_HpkeLabeledExtract function during ECH (Encrypted Client Hello) processing. A malicious TLS server can send an oversized ECH config that overflows a stack-allocated buffer, potentially enabling remote code execution or causing client crash.

MitigationUpgrade to a patched wolfSSL version, or if ECH is not required, ensure it remains disabled (it is off by default).

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:>= 5.6.0, < 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. Check wolfSSL version
    Run `wolfssl version` or `wolfssl -version` to display the installed version, or inspect the wolfssl/version.h header file
    Affected if The version is 5.6.0 or higher but lower than 5.9.0
  2. Verify ECH support is compiled in
    Check build configuration or headers for HAVE_ECH or WOLFSSL_ECH definitions, or run `wolfssl ciphers` and look for ECH-related ciphersuites
    Affected if ECH support was enabled at compile time (HAVE_ECH defined)
  3. Confirm ECH is actually enabled at runtime
    Inspect application configuration, TLS handshake settings, or verify no explicit ECH disable flag is set in the client configuration
    Affected if ECH is actively enabled in the TLS client configuration (not just compiled in)
  4. Check for oversized ECH config in network traffic
    Capture TLS handshake traffic with Wireshark or tcpdump and examine the Encrypted ClientHello extension length field
    Affected if A TLS server sends an ECH config extension with length exceeding the expected buffer size

You are affected if wolfSSL version is between 5.6.0 and 5.8.x AND ECH is enabled (compiled in and actively used by the client).

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

Upgrade to a patched wolfSSL version, or if ECH is not required, ensure it remains disabled (it is off by default).

Recommended fix High confidence

wolfSSL >= 5.9.0

  1. Identify current wolfSSL version by checking your project's dependency or running 'wolfssl version' if binary available
  2. Upgrade wolfSSL to version 5.9.0 or later by updating the dependency in your build system (e.g., package manager, submodule, or source download)
  3. Rebuild and redeploy the application to incorporate the fixed library version
  4. If using a package manager (apt, yum, brew, conan, vcpkg), run the equivalent of 'wolfssl upgrade to >=5.9.0' or reinstall the package
  5. Verify the new version is loaded correctly by checking runtime library version or running 'wolfssl version'
  6. If ECH is not required in production, consider disabling it with '--disable-ech' at compile time as an additional hardening measure
  7. Test the application functionality to ensure the upgrade does not break existing TLS/ECH operations
Caveat ECH (Encrypted Client Hello) functionality remains available but ensure server-side ECH support is trustworthy; no breaking API changes expected from this security fix

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

Fix this in Wolfssl Scoped from the published advisory
  • Consultation3.0 h
  • Implementation4.0 h
  • Testing6.0 h
  • Review / QA3.0 h
16.0 hours of engineering $2,760
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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-2026-3849 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