CVE-2025-6291 Overview
CVE-2025-6291 is a stack-based buffer overflow vulnerability in the D-Link DIR-825 wireless router running firmware version 2.03. The flaw resides in the do_file function within the HTTP POST request handler. An attacker can manipulate input to the function and corrupt the stack, potentially achieving remote code execution on the device. The vulnerability is reachable over the network and a public proof-of-concept has been disclosed. D-Link no longer supports this product, so no official vendor patch will be released. The weakness is categorized under CWE-119, improper restriction of operations within the bounds of a memory buffer.
Critical Impact
Remote attackers can corrupt the router's stack through crafted HTTP POST requests, enabling code execution on an end-of-life device that will not receive a vendor patch.
Affected Products
- D-Link DIR-825 hardware router
- D-Link DIR-825 firmware version 2.03
- All deployments running the affected do_file HTTP POST handler
Discovery Timeline
- 2025-06-20 - CVE-2025-6291 published to NVD
- 2026-06-17 - Last updated in NVD database
Technical Details for CVE-2025-6291
Vulnerability Analysis
The vulnerability exists in the do_file function of the HTTP POST request handler in the DIR-825 web management interface. The function processes attacker-controllable POST data without enforcing proper bounds on a fixed-size stack buffer. Supplying an oversized payload overruns the buffer and overwrites adjacent stack memory, including saved return addresses on the MIPS architecture used by the device.
Because the router's HTTP daemon typically runs with elevated privileges and lacks modern exploit mitigations such as stack canaries, ASLR, and non-executable stacks on consumer firmware, successful exploitation can lead to arbitrary code execution. An attacker authenticated to the management interface, or one positioned to reach the management interface on the LAN or WAN if exposed, can trigger the condition.
Root Cause
The root cause is missing length validation on user-supplied POST parameters before they are copied into a stack-allocated buffer inside do_file. This is a classic [CWE-119] memory boundary violation. Because the device is end-of-life, the maintainer will not issue corrected firmware addressing the unsafe copy.
Attack Vector
The attack vector is network-based. An attacker sends a crafted HTTP POST request to the router's web management interface with an oversized parameter targeting the vulnerable handler. The exploit has been disclosed publicly, increasing the risk of opportunistic scanning and exploitation. Technical details and proof-of-concept material are documented in the GitHub vulnerability findings repository and tracked as VulDB #313293.
Detection Methods for CVE-2025-6291
Indicators of Compromise
- Unexpected HTTP POST requests to the DIR-825 web management interface containing unusually long parameter values.
- Crashes or reboots of the router's httpd process correlated with inbound HTTP traffic.
- Outbound connections initiated from the router to unfamiliar hosts, suggesting post-exploitation activity.
- Configuration changes to DNS, firewall, or administrative credentials that were not made by an authorized administrator.
Detection Strategies
- Monitor network traffic to and from DIR-825 devices for malformed or oversized HTTP POST bodies directed at the management interface.
- Inspect router syslog output forwarded to a central collector for repeated daemon restarts or memory faults.
- Deploy IDS/IPS signatures that match large POST parameter lengths against the do_file endpoint pattern.
Monitoring Recommendations
- Forward router logs to a central log analytics platform and alert on HTTP daemon crashes.
- Baseline normal management-interface traffic and alert on anomalous request volumes or sizes.
- Track and inventory legacy D-Link devices on the network so end-of-life assets are visible to security operations.
How to Mitigate CVE-2025-6291
Immediate Actions Required
- Disconnect or replace DIR-825 routers running firmware 2.03, as the product is end-of-life and will not receive a fix.
- Disable WAN-side access to the router's web management interface immediately.
- Restrict LAN-side management access to a dedicated administrative VLAN or trusted host.
- Rotate administrative credentials and any pre-shared keys configured on the device.
Patch Information
No patch is available. D-Link has declared the DIR-825 end-of-life, and the advisory explicitly states that the affected product is no longer supported by the maintainer. The only durable remediation is to retire the device and replace it with a currently supported router model. Vendor information is available at the D-Link official site.
Workarounds
- Block inbound HTTP and HTTPS traffic to the router's management interface at an upstream firewall.
- Segment the router away from sensitive internal assets until it can be decommissioned.
- Apply ACLs that permit management access only from a single hardened administrative workstation.
- Disable remote administration features and UPnP if they are not strictly required.
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
