CVE-2026-76652 in TL-MR6400
Summary
by MITRE • 09/10/2026
An authenticated directory traversal vulnerability in file upload functionality has been identified in Archer MR600 (v2, v3 & v5) and TL-MR6400 v8. Due to insufficient validation of user-supplied file information, an authenticated remote attacker with access to the affected upload functionality could upload a specially crafted file and cause it to be written outside the intended directory.
Successful exploitation could allow an authenticated remote attacker to write files to unintended locations, potentially overwriting or modifying files accessible to the affected service; arbitrary code execution has not been demonstrated.
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Analysis
by VulDB Data Team • 09/10/2026
The identified vulnerability represents a critical security flaw within the file upload mechanisms of Archer MR600 versions 2 through 5 and TL-MR6400 version 8, classified technically as an authenticated directory traversal attack. This issue stems from insufficient validation of user-supplied file information during the ingestion process. In standard secure implementations, uploaded files are confined to a specific sandbox or upload directory to prevent interference with system-critical components. However, in these affected devices, the application fails to properly sanitize path separators or relative navigation sequences provided by the client. This allows an attacker who has already obtained valid authentication credentials to manipulate the file destination path, effectively bypassing the intended containment boundaries and writing files to arbitrary locations on the device's filesystem that are accessible to the service account running the upload functionality.
From a technical perspective, this flaw aligns with CWE-22: Improper Limitation of a Pathname to a Restricted Directory. The core failure lies in the application logic not stripping or validating directory traversal characters such as dot-dot-slash sequences before processing the file write operation. Because the vulnerability requires authentication, it is categorized under attacker prerequisites that involve valid user credentials rather than unauthenticated remote exploitation. This distinction places the risk profile differently compared to unauthenticated vulnerabilities, yet it remains severe because many IoT and networking devices often have accounts with elevated privileges or broad filesystem access rights for administrative functions. The ability to write files outside the intended directory means an attacker can potentially overwrite configuration files, inject malicious scripts into web-accessible directories if such paths are reachable through traversal, or corrupt system logs and other critical data structures managed by the service.
The operational impact of this vulnerability is significant due to its potential for privilege escalation and persistence within the network environment. Although arbitrary code execution has not been explicitly demonstrated in initial reports, the capability to write files to unintended locations creates a high-risk pathway for further exploitation. An attacker could overwrite existing binaries or configuration scripts with malicious versions that execute upon service restarts or specific triggers. This can lead to unauthorized access control bypasses, data integrity violations, and potential denial of service conditions if critical system files are corrupted. Furthermore, the ability to place web shells in accessible directories could facilitate remote code execution without requiring additional vulnerabilities, effectively turning this file write issue into a full device compromise vector depending on the specific filesystem permissions and server configurations present in the Archer MR600 or TL-MR6400 deployments.
In terms of threat modeling and industry standards, this vulnerability maps to MITRE ATT&CK technique T1537: Transfer Data to Cloud Account if cloud sync is involved, but more directly relates to Local File Inclusion concepts adapted for server-side file writes, often associated with the Initial Access or Persistence tactics depending on how the written files are utilized. It reflects a common pattern in embedded systems where input validation is overlooked during development cycles focused on feature delivery rather than security hardening. The lack of demonstrated arbitrary code execution does not mitigate the risk; it merely indicates that the immediate exploit chain requires additional steps, such as leveraging other local vulnerabilities or misconfigurations to achieve full control.
Mitigation strategies should prioritize immediate patching by the vendor if an official update is available, which typically involves correcting the input validation logic in the file upload handler to strictly whitelist allowed characters and enforce canonical path resolution before writing files. Administrators of affected devices must ensure that all administrative accounts use strong, unique passwords to reduce the likelihood of credential compromise leading to this vulnerability's exploitation. Network segmentation should be employed to limit access to management interfaces from untrusted networks, ensuring that only authorized administrators can reach the upload functionality. Additionally, monitoring file system integrity and reviewing logs for unusual write operations outside standard directories can help detect potential attempts at exploiting this flaw before significant damage occurs until a permanent software fix is deployed.