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CVE Record

CVE-2026-12221: Yealink SIP-T46U Firmware Chunk Upload upgrade sprintf stack-based overflow

A 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 but did not respond in any way.

HighCVSS 8.6Not KEV-listed Updated
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Glexia's Take high

Analyst readout for executives and security teams

Plain-English summary

CVE-2026-12221 is a high-severity flaw in Yealink SIP-T46U firmware version 108.86.0.118. A local-network attacker with low privileges could trigger a stack buffer overflow during firmware chunk upload handling. Public exploit material is reported, but the provided sources do not show active exploitation or a vendor patch.

Executive priority

Treat as urgent for environments with Yealink SIP-T46U phones on shared internal networks. Prioritize inventory, segmentation, and access review now. Patch guidance is not available in the provided sources, so remediation depends on vendor updates or compensating controls.

Technical view

VulDB describes a stack-based buffer overflow in /api/upgrade/upgrade, within the Firmware Chunk Upload Handler, involving sprintf and manipulation of uid/start_offset. The CVSS 4.0 score is 8.6, with adjacent-network access, low complexity, low privileges, no user interaction, and high confidentiality, integrity, and availability impact.

Likely exposure

Organizations using Yealink SIP-T46U phones running firmware 108.86.0.118 are the known exposure. Risk is concentrated on internal or adjacent networks where attackers can reach the phone management or upgrade interface and have low-level authenticated access.

Exploitation context

Sources state the attack must be approached from the local network and that exploit material has been made public. CVE KEV status is false in the provided bundle, and no cited source confirms active exploitation in the wild.

Researcher notes

Evidence is mainly from VulDB and CVE records. The vendor reportedly did not respond to early disclosure. The affected version is specifically 108.86.0.118. No source in the bundle confirms a fixed version, active exploitation, or broader Yealink model impact.

Mitigation direction

  • Identify Yealink SIP-T46U devices and confirm firmware versions.
  • Restrict phone management and upgrade interfaces to trusted administration networks.
  • Limit low-privilege accounts with access to upgrade functions.
  • Monitor Yealink and VulDB for vendor guidance or fixed firmware.
  • Avoid exposing phone administration interfaces to guest or user VLANs.

Validation and detection

  • Inventory SIP-T46U phones across voice and office networks.
  • Check each device for firmware version 108.86.0.118.
  • Review network ACLs controlling access to phone management services.
  • Review logs for unusual firmware upload or upgrade activity.
  • Track vendor advisories before applying any upgrade-related changes.
Prepared
Confidence
medium
Sources
6

Public sources used

Based on public source material and reviewed before publication.

Potential ATT&CK relevance

Conservative CVE-to-ATT&CK context

These mappings and lookup hints may be relevant to the vulnerability behavior, CWE, affected product, or exposure path. Glexia-inferred context is not an official MITRE, ATT&CK, CWE, or CVE Program mapping.

ATT&CK lookup starting points

Use these exact CWE pages and searches to review the Glexia ATT&CK library from this CVE's weakness and description context.

cwe · low confidence lookup

CWE-119: Exact CWE lookup

Use the exact CWE identifier as the starting point before reviewing related ATT&CK behavior. Open the exact CWE lookup page first, then review the ATT&CK searches from that MITRE weakness context. This is a Glexia lookup hint, not an official ATT&CK mapping.

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cwe · low confidence lookup

CWE-121: Exact CWE lookup

Use the exact CWE identifier as the starting point before reviewing related ATT&CK behavior. Open the exact CWE lookup page first, then review the ATT&CK searches from that MITRE weakness context. This is a Glexia lookup hint, not an official ATT&CK mapping.

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cve · low confidence lookup

CVE-2026-12221 mapping review

Open the CVE-to-ATT&CK bridge for reviewed, inferred, or future official mappings tied to this CVE.

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Vulnerability profile CVE Program record
Severity
High
CVSS
8.6 (4.0)
Known Exploited
No
Published

Vector: CVSS:4.0/AV:A/AC:L/AT:N/PR:L/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N/E:P

Official CVE source material

CNA and ADP enrichment extracted from CVE v5

These fields come from the CVE record and ADP containers, not from Glexia's Take. They preserve time-varying source decisions such as CISA SSVC, KEV status, CVSS metrics, and provider references.

4 CVSS vectors
6 Timeline events
0 ADP providers
6 Source links

CVSS vector scores

4 official scores

We collect every scored CVSS vector available in the official CNA and ADP containers. When more than one version is present, the table keeps the source vectors side by side instead of collapsing them into the highest score.

Score Version Severity Vector Exploit Impact Source
8.6 CVSS 4.0 High CVSS:4.0/AV:A/AC:L/AT:N/PR:L/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N/E:P — — VulDB
8 CVSS 3.1 High CVSS:3.1/AV:A/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H/E:P/RL:X/RC:R 2.1 5.9 VulDB
8 CVSS 3.0 High CVSS:3.0/AV:A/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H/E:P/RL:X/RC:R 2.1 5.9 VulDB
7.7 CVSS 2.0 High AV:A/AC:L/Au:S/C:C/I:C/A:C/E:POC/RL:ND/RC:UR 5.1 10 VulDB

Vulnerability scoring details

Base CVSS 4.0 score

8.6 High
CVSS 4.0 vector shape for CVE-2026-12221 Attack VectorAttack ComplexityAttack RequirementsPrivileges RequiredUser InteractionVS ConfidentialityVS IntegrityVS AvailabilitySS ConfidentialitySS IntegritySS Availability

Vector: CVSS:4.0/AV:A/AC:L/AT:N/PR:L/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N/E:P

Attack Vector
NetworkAdjacentLocalPhysical
Attack Complexity
LowHigh
Attack Requirements
NonePresent
Privileges Required
NoneLowHigh
User Interaction
NonePassiveActive
VS Confidentiality
HighLowNone
VS Integrity
HighLowNone
VS Availability
HighLowNone
SS Confidentiality
HighLowNone
SS Integrity
HighLowNone
SS Availability
HighLowNone

Vulnerability timeline

Timeline events are normalized from CVE metadata, CNA source timelines, ADP timelines, and KEV metadata when present.

  1. Source timeline VulDB

    Advisory disclosed

  2. Source timeline VulDB

    VulDB entry created

  3. CVE reserved CVE Program

    The CVE ID was reserved by the assigning CNA.

  4. Source timeline VulDB

    VulDB entry last update

  5. CVE published CVE Program

    The CVE record was published.

  6. CVE updated CVE Program

    The CVE record metadata indicates this as the latest update time.

Source materials

Affected products

Products and packages named in the record

Vendor Product Version / package Status
Yealink SIP-T46U 108.86.0.118 Listed
Weakness

CWE details

CWE-119CWE-121

CWE links open Glexia weakness intelligence pages with official CWE context, developer remediation guidance, and related CVE mappings.

CWE-119 · source CWE mapping

Improper Restriction of Operations within the Bounds of a Memory Buffer

Improper Restriction of Operations within the Bounds of a Memory Buffer represents a recurring weakness pattern that can create exploitable paths when design, validation, or implementation controls are missing.

Open CWE intelligence Same-CWE CVEs
CWE-121 · source CWE mapping

Stack-based Buffer Overflow

Stack-based Buffer Overflow represents a recurring weakness pattern that can create exploitable paths when design, validation, or implementation controls are missing.

Open CWE intelligence Same-CWE CVEs