Analyst readout for executives and security teams
Plain-English summary
CVE-2026-12220 affects Yealink SIP-T46U firmware 108.86.0.118. A local-network attacker with low privileges could trigger a stack-based buffer overflow in a firmware chunk upload API. The public record says exploit details were disclosed, but there is no KEV listing or cited evidence of active exploitation.
Executive priority
Treat as high priority for environments using Yealink SIP-T46U phones. The issue has high potential device impact and public exploit disclosure, but appears local-network constrained. Prioritize inventory, segmentation, and monitoring for vendor updates.
Technical view
The flaw is in /api/upgrade/accupgradebychunk, function mod_upgrade.SparePartsUpload, where manipulation of the uid argument can cause a stack-based buffer overflow. VulDB rates it CVSS 4.0 8.6 with adjacent-network access, low complexity, low privileges, no user interaction, and high impact to vulnerable-system confidentiality, integrity, and availability.
Likely exposure
Exposure is likely limited to Yealink SIP-T46U phones running firmware 108.86.0.118 reachable from an attacker on the same local network segment. Internet exposure is not indicated by the provided sources.
Exploitation context
The source states the attack can only be initiated within the local network and that an exploit has been publicly disclosed. No source in the bundle confirms active exploitation in the wild.
Researcher notes
Evidence comes primarily from VulDB and CVE records. Vendor response and official fix status are not provided in the source bundle. Avoid assuming broader Yealink model impact beyond SIP-T46U firmware 108.86.0.118.
Mitigation direction
- Inventory Yealink SIP-T46U devices and identify firmware version 108.86.0.118.
- Restrict management and upgrade API access to trusted administration networks.
- Monitor Yealink and VulDB for vendor guidance or patched firmware.
- Segment VoIP devices from user and guest networks where feasible.
- Review local network access controls for untrusted or compromised hosts.
Validation and detection
- Confirm whether any SIP-T46U devices run firmware 108.86.0.118.
- Check whether /api/upgrade/accupgradebychunk is reachable from non-admin network segments.
- Review device logs for unexpected firmware upload or upgrade activity.
- Verify VoIP network segmentation limits access to phone management interfaces.
- Track CVE and vendor advisories for updated remediation details.
Public sources used
Based on public source material and reviewed before publication.
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-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.
Open ATT&CK lookupCWE-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.
Open ATT&CK lookupCVE-2026-12220 mapping review
Open the CVE-to-ATT&CK bridge for reviewed, inferred, or future official mappings tied to this CVE.
Open ATT&CK lookup- 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
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.
CVSS vector scores
4 official scoresWe 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.
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 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 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 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 HighVector: 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
Base CVSS 3.1 score
8 HighVector: 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
Base CVSS 3.0 score
8 HighVector: 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
Base CVSS 2.0 score
7.7 HighVector: AV:A/AC:L/Au:S/C:C/I:C/A:C/E:POC/RL:ND/RC:UR
Vulnerability timeline
Timeline events are normalized from CVE metadata, CNA source timelines, ADP timelines, and KEV metadata when present.
- Source timeline VulDB
Advisory disclosed
- Source timeline VulDB
VulDB entry created
- CVE reserved CVE Program
The CVE ID was reserved by the assigning CNA.
- Source timeline VulDB
VulDB entry last update
- CVE published CVE Program
The CVE record was published.
- CVE updated CVE Program
The CVE record metadata indicates this as the latest update time.
Source materials
- CVE List V5 source CVE List V5
- VDB-370863 | Yealink SIP-T46U Firmware Chunk Upload handler accupgradebychunk mod_upgrade.SparePartsUpload stack-based overflow CVE reference, VulDB · vdb-entry, technical-description
- VDB-370863 | CTI Indicators (IOB, IOC, IOA) CVE reference, VulDB · signature, permissions-required
- CVE-2026-12220 | CVE Analysis and Report CVE reference, VulDB · third-party-advisory
- Submit #834205 | yealink T46U 108.86.0.118 Stack-based Buffer Overflow CVE reference, VulDB · third-party-advisory
- http://cdn2.v50to.cc/T46U/T46U_mod_upgrade_SparePartsUpload_stack_overflow.zip CVE reference, VulDB · broken-link, exploit
Products and packages named in the record
CWE details
CWE links open Glexia weakness intelligence pages with official CWE context, developer remediation guidance, and related CVE mappings.
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.
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.