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Out-of-bounds WriteWeakness · CWE-787

CVE-2025-3873

MEDIUM · 6.0 CVSS v4.0 Published 2025-07-25
Mitigation only
No fix yet — a mitigation exists. There is no fixed release. A documented workaround reduces exposure in the meantime.
See remediation →
66/100
Remediation priority · Elevated
Remotely reachable 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
The following APIs for the Silcon Labs SiWx91x prior to vesion 3.4.0 failed to check the size of the output buffer of the caller which could lead to data corruption on the host (Cortex-M4) application. sl_si91x_aes sl_si91x_gcm sl_si91x_ccm sl_si91x_sha

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

The Silicon Labs SiWx91x cryptographic APIs (sl_si91x_aes, sl_si91x_gcm, sl_si91x_ccm, sl_si91x_sha) prior to version 3.4.0 fail to validate the caller's output buffer size before writing encrypted or hashed data. This missing bounds check can cause data to be written beyond the allocated buffer, leading to memory corruption on the host Cortex-M4 application.

MitigationUpgrade the SiWx91x firmware to version 3.4.0 or later, which implements proper output buffer size validation in the affected cryptographic APIs.

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

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
High
Privileges
Low
Authentication
X
User interaction
None
Scope
X

CVSS:4.0/AV:N/AC:H/AT:N/PR:L/UI:N/VC:L/VI:H/VA:N/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X

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 SiWx91x firmware or SDK version
    Locate the SiWx91x firmware image, SDK manifest, or library files and retrieve the version identifier (check firmware header, SDK release notes, or library file properties)
    Affected if Version is present and less than 3.4.0
  2. Check for sl_si91x_aes API usage
    Search source code or binary for calls to sl_si91x_aes function (inspect disassembly or grep source files for the function name)
    Affected if The API is called and firmware version is below 3.4.0
  3. Check for sl_si91x_gcm API usage
    Search source code or binary for calls to sl_si91x_gcm function (inspect disassembly or grep source files for the function name)
    Affected if The API is called and firmware version is below 3.4.0
  4. Check for sl_si91x_ccm API usage
    Search source code or binary for calls to sl_si91x_ccm function (inspect disassembly or grep source files for the function name)
    Affected if The API is called and firmware version is below 3.4.0
  5. Check for sl_si91x_sha API usage
    Search source code or binary for calls to sl_si91x_sha function (inspect disassembly or grep source files for the function name)
    Affected if The API is called and firmware version is below 3.4.0

You are affected if your SiWx91x firmware or SDK version is prior to 3.4.0 and your application uses any of the vulnerable cryptographic APIs (sl_si91x_aes, sl_si91x_gcm, sl_si91x_ccm, or sl_si91x_sha).

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
Mitigation available No clean upgrade yet — mitigate in the meantime
Mitigation

Upgrade the SiWx91x firmware to version 3.4.0 or later, which implements proper output buffer size validation in the affected cryptographic APIs.

Recommended fix High confidence

SiWx91x firmware version 3.4.0 or later

  1. Obtain the SiWx91x firmware version 3.4.0 or later from Silicon Labs (via Simplicity Studio, direct download, or SDK update)
  2. Review the SiWx91x migration guide or release notes for version 3.4.0 to understand any API changes or configuration updates required
  3. Update the host (Cortex-M4) application to use the updated SiWx91x library/binary containing version 3.4.0
  4. If using an OTA (Over-The-Air) update mechanism, deploy the updated firmware to SiWx91x devices in the field
  5. After upgrading, verify that the cryptographic APIs (sl_si91x_aes, sl_si91x_gcm, sl_si91x_ccm, sl_si91x_sha) now properly validate output buffer sizes before writing
Caveat Review release notes for version 3.4.0; firmware upgrades may include API changes requiring host application updates

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

Have this fixed Scoped from the published advisory
  • Consultation2.0 h
  • Implementation4.0 h
  • Testing6.0 h
  • Review / QA3.0 h
15.0 hours of engineering $2,560
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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-2025-3873 in production — separate from our analysis above.

No notes yet

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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