CVE-2026-7208

Executive Summary

CVE-2026-7208 is a race condition vulnerability (CWE-362) affecting Yealink SIP-T33G IP phones running firmware versions 124.86.x.x prior to 124.87.0.0. Authenticated attackers can exploit this flaw to interrupt active diagnostic processes by concurrently deleting output files written to predictable paths under the diagnostic directory. Successful exploitation leaves the system in an inconsistent state, causing a high availability impact (CVSS 5.3, AV:N/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H), though no public proof-of-concept or active exploitation has been observed.

Technical Analysis

This vulnerability is a classic time-of-check to time-of-use (TOCTOU) race condition rooted in CWE-362: Concurrent Execution using Shared Resource with Improper Synchronization. The affected component is the diagnostic subsystem of the Yealink SIP-T33G firmware. When an authenticated user initiates a diagnostic operation—such as traceroute or ping—the device writes output to files at predictable paths under the diagnostic directory. The vulnerability arises because the file deletion endpoint can be invoked concurrently with a running diagnostic process, allowing the deletion of output files while they are still being written or actively used by the diagnostic process.

The race condition exists because the system does not properly synchronize access to diagnostic output files between the running diagnostic process and the file deletion endpoint. An attacker who is already authenticated (PR:L) can trigger a diagnostic operation and simultaneously invoke the file deletion endpoint. The concurrent deletion causes the diagnostic process to fail due to missing or inaccessible output files, terminating the process prematurely and leaving the system in an inconsistent state. The attack complexity is rated High (AC:H) because successful exploitation requires precise timing to win the race condition.

The network attack vector (AV:N) indicates the vulnerable interfaces are accessible over the network, consistent with the web-based management interface typically present on enterprise IP phones. The scope is unchanged (S:U), meaning the impact is confined to the vulnerable component itself. There is no confidentiality (C:N) or integrity (I:N) impact; the sole impact is availability (A:H), reflecting the potential to disrupt diagnostic operations and leave the device in an unstable state.

The specific diagnostic directory path and file naming convention are not detailed in the available NVD description. The vulnerability class—race condition in diagnostic file handling—is well understood: the attacker must have valid credentials to access the diagnostic and file management interfaces, and the attack requires the ability to execute two operations concurrently. The predictable nature of output file paths is a key enabling factor, as it allows the attacker to know exactly which file to target for deletion.

The firmware version range 124.86.x.x prior to 124.87.0.0 suggests the vulnerability was introduced in the 124.86 branch and addressed in 124.87.0.0. However, no patch evidence has been identified from any tracked source, and the patch confidence is 0/4 (UNPATCHED). This means no official fix is confirmed to exist, and no workarounds are documented.

Exploitation Scenarios

The attack chain for CVE-2026-7208 requires an authenticated attacker with network access to the device's management interface. No public PoC is available; the attack chain is inferred from the vulnerability class (CWE-362) and the NVD description.

1. Reconnaissance/target identification: The attacker identifies Yealink SIP-T33G devices on the network, likely through network scanning or Shodan queries targeting the product. The attacker must obtain valid credentials for the device's management interface, either through default credentials, credential reuse, or prior compromise. The devices are typically deployed in enterprise VoIP environments.

2. Triggering the specific flaw class: The attacker authenticates to the device and accesses the diagnostic functionality. The attacker initiates a diagnostic operation such as traceroute or ping, which causes the device to write output files to predictable paths under the diagnostic directory. Concurrently, the attacker invokes the file deletion endpoint to delete those same output files. The race condition occurs because the system does not properly synchronize the running diagnostic process with the file deletion operation.

3. Payload/execution method at the vulnerability-class level: The exploit is a timing-based attack. The attacker must send the diagnostic initiation request and the file deletion request in a way that the deletion occurs while the diagnostic process is still writing to or using the output file. This requires precise timing and may involve repeated attempts to win the race. The predictable file paths under the diagnostic directory enable the attacker to target the correct file without needing to discover its name dynamically.

4. Post-exploitation impact: Successful exploitation interrupts the active diagnostic process, terminating it prematurely. The system is left in an inconsistent state, which may require a reboot or manual intervention to restore normal operation. The availability impact is high (A:H), meaning the diagnostic functionality is rendered unavailable and the device may experience broader instability. There is no confidentiality or integrity impact, so the attacker cannot directly read or modify sensitive data through this flaw alone. The attacker could potentially use this as a denial-of-service primitive against diagnostic operations, but the requirement for authentication limits the blast radius to compromised or insider accounts.

Impact Assessment

The business impact of CVE-2026-7208 is primarily operational. Affected organizations are those deploying Yealink SIP-T33G IP phones with firmware versions 124.86.x.x prior to 124.87.0.0. These devices are commonly used in enterprise VoIP deployments, contact centers, and unified communications environments. The CVSS score of 5.3 (Medium) reflects the high attack complexity and authentication requirement, but the availability impact is High (A:H), meaning a successful attack can disrupt diagnostic operations and potentially cause device instability.

The blast radius is limited to the individual device targeted, as the scope is unchanged (S:U). However, in a large deployment, an attacker with credentials could target multiple devices to cause widespread disruption of diagnostic capabilities. The lack of confidentiality and integrity impact means the attacker cannot exfiltrate data or modify configurations through this vulnerability alone. The primary risk is to the availability of diagnostic functions, which are typically used for troubleshooting and network monitoring. If diagnostic operations are part of critical monitoring or SLA-backed services, the business impact could be more significant.

The EPSS score of 0.00347 (25.4th percentile) indicates a low probability of exploitation in the wild in the next 30 days. There is no CISA KEV listing, no public PoC, no Nuclei template, and no exploit code available. This suggests the vulnerability is not currently a high-priority target for threat actors, but the lack of a patch increases the risk over time.

Detection Guidance

Sigma Rule

title: Yealink SIP-T33G Diagnostic File Deletion Race Condition
id: 7a8b9c0d-1e2f-3a4b-5c6d-7e8f9a0b1c2d
status: experimental
description: Detects concurrent diagnostic initiation and file deletion requests targeting Yealink SIP-T33G diagnostic directory
references:
  - https://nvd.nist.gov/vuln/detail/CVE-2026-7208
author: Threat Intelligence
date: 2026-01-01
tags:
  - attack.t1489
logsource:
  category: webserver
  product: yealink
detection:
  selection_diagnostic:
    cs-method: 'POST'
    cs-uri-query|contains:
      - 'traceroute'
      - 'ping'
  selection_delete:
    cs-method: 'POST'
    cs-uri-query|contains:
      - 'delete'
      - 'remove'
  timeframe: 5s
  condition: selection_diagnostic and selection_delete
falsepositives:
  - Legitimate administrative diagnostic operations with cleanup
level: medium

YARA Rule

rule CVE_2026_7208_Yealink_Race_Condition
{
    meta:
        description = "Detects Yealink SIP-T33G firmware 124.86.x.x diagnostic race condition indicators"
        author = "Threat Intelligence"
        date = "2026-01-01"
        reference = "https://nvd.nist.gov/vuln/detail/CVE-2026-7208"
        cve = "CVE-2026-7208"
    strings:
        $fw_ver = "124.86." ascii wide
        $diag_dir = "diagnostic" ascii wide nocase
        $traceroute = "traceroute" ascii wide nocase
        $ping = "ping" ascii wide nocase
        $delete_endpoint = "delete" ascii wide nocase
    condition:
        $fw_ver and $diag_dir and ( $traceroute or $ping ) and $delete_endpoint
}

Suricata IDS Rule

alert http $HOME_NET any -> $EXTERNAL_NET any (msg:"CVE-2026-7208 Yealink SIP-T33G Diagnostic Race Condition Attempt"; flow:to_server,established; content:"POST"; http_method; content:"traceroute"; http_uri; nocase; content:"delete"; http_uri; nocase; classtype:attempted-dos; reference:cve,2026-7208; sid:2026720801; rev:1;)

Elastic Detection

sequence by source.ip with maxspan=5s
  [http where http.request.method == "POST" and http.request.uri contains "traceroute"]
  [http where http.request.method == "POST" and http.request.uri contains "delete"]

Splunk SPL Query

index=web sourcetype=yealink_access
| search (uri_path="*traceroute*" OR uri_path="*ping*") AND uri_path="*delete*"
| stats count min(_time) as firstTime max(_time) as lastTime by src_ip, uri_path, status
| where count > 1
| convert ctime(firstTime) ctime(lastTime)

Wazuh OSSEC Rule

<group name="yealink,cve-2026-7208,">
  <rule id="100720" level="10">
    <decoded_as>json</decoded_as>
    <field name="url">\.*(traceroute|ping).*</field>
    <field name="url">\.*delete.*</field>
    <description>CVE-2026-7208: Yealink SIP-T33G diagnostic file deletion race condition attempt</description>
    <mitre>
      <id>T1489</id>
    </mitre>
    <group>dos,</group>
  </rule>
</group>

Mitigation & Patch Guidance

Patch confidence: 0/4 (UNPATCHED — no patch evidence from any tracked source).

1. Immediate mitigations:

   • Restrict network access to the Yealink SIP-T33G management interface to trusted management VLANs or specific administrative IP addresses.
   • Enforce strong, unique administrative credentials to prevent unauthorized access (PR:L requirement).
   • Disable or restrict diagnostic functionality (traceroute, ping) and file deletion endpoints if not operationally required.
   • Monitor for concurrent diagnostic initiation and file deletion requests as a potential attack indicator.
   • Isolate affected devices on segregated network segments to limit lateral movement and reduce exposure.

2. Patch/upgrade steps:

   • Monitor the Yealink security advisory page for firmware version 124.87.0.0 or later, which is referenced as the fixed target version.
   • Once available, upgrade all affected SIP-T33G devices to firmware version 124.87.0.0 or later.
   • Verify the firmware version after upgrade and confirm the diagnostic file handling race condition is resolved.
   • If no patch becomes available, consider replacing affected devices with alternative models or vendors.

3. Long-term hardening:

   • Implement network segmentation for VoIP devices, placing them on dedicated VLANs with strict access controls.
   • Deploy continuous monitoring for race condition exploitation attempts across all management interfaces.
   • Establish a firmware update management process to ensure timely patching of VoIP infrastructure.
   • Conduct regular security assessments of VoIP devices, including authentication strength and exposed management interfaces.
   • Consider replacing end-of-support devices with models that receive regular security updates.

References

• NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-7208
• CWE-362: https://cwe.mitre.org/data/definitions/362.html
• Yealink Security Advisory: Refer to Yealink official security advisory page for firmware 124.87.0.0 (no direct URL available in provided data)
• CISA KEV: Not applicable (CVE not listed)
• EPSS: 0.00347 (25.4th percentile) — https://www.first.org/epss/
• No known threat actor campaigns or exploit-in-the-wild evidence available.