CVE-2026-12221
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 · uneditedA vulnerability was found in Yealink SIP-T46U 108.86.0.118. This impacts the function sprintf of the file /api/upgrade/upgrade of the component Firmware Chunk Upload Handler. Performing a manipulation of the argument uid/start_offset results in stack-based buffer overflow. The attack needs to be approached within the local network. The exploit has been made public and could be used. The vendor was contacted early about this disclosure and is working on a patch to fix it.
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 confidenceStack-based buffer overflow vulnerability in Yealink SIP-T46U firmware (v108.86.0.118) in the sprintf function of the Firmware Chunk Upload Handler (/api/upgrade/upgrade). The overflow is triggered via manipulated uid/start_offset arguments during firmware upload operations. Attack requires local network access and a public exploit exists.
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
- Adjacent
- Complexity
- Low
- Privileges
- Low
- User interaction
- None
- Scope
- Unchanged
- Confidentiality
- High
- Integrity
- High
- Availability
- High
CVSS:3.1/AV:A/AC:L/PR:L/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 checksWork through these to decide whether this CVE applies to you.
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Identify the device modelAccess the phone web interface or check the device label to confirm it is a Yealink SIP-T46U modelAffected if The device is a Yealink SIP-T46U IP phone
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Check the firmware versionLog into the phone web interface and navigate to Settings > Status > Firmware Version, or use the phone menu to find the firmware versionAffected if The installed firmware version is v108.86.0.118 or any version prior to the patched release
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Verify the upgrade API endpoint existsAttempt to access https://<phone_ip>/api/upgrade/upgrade or check the phone configuration for enabled upgrade APIsAffected if The /api/upgrade/upgrade endpoint is present and accessible on the device
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Check network accessibilityReview network segmentation and VLAN placement. Determine if untrusted local network hosts can reach the phone's HTTP interface on port 80/443Affected if The device HTTP interface is reachable from network segments accessible to untrusted users or guest devices
You are affected if you have a Yealink SIP-T46U with firmware v108.86.0.118 or lower that has the /api/upgrade/upgrade endpoint exposed to accessible network segments.
Generated from the published advisory. Verify against your own configuration.
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.
From vendor dataSince no vendor patch is available, implement network segmentation to restrict access to the device's management interface to trusted IPs only, and monitor for indicators of exploitation until an official firmware update is released.
- Consultation4.0 h
- Implementation8.0 h
- Testing4.0 h
- Review / QA2.0 h
An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $5,120.
Scan for this in your stack
Free · runs locallyCheck whether your project pulls in CVE-2026-12221 — or any other known-vulnerable package — straight from your lock files. Free and open source; it runs locally and uploads nothing.
References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.
Primary sourcesPractitioner notes
ContributedPeer-ranked notes from engineers who’ve handled CVE-2026-12221 in production — separate from our analysis above.
The advisory tells you what broke. It rarely tells you what actually worked. If you’ve dealt with this one, that detail is what the next engineer is searching for.
- The version that genuinely resolved it — not the one the vendor claimed
- A config change or rule that shut the vector down
- A gotcha in the upgrade path that cost you an afternoon
No notes yet
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- 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
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