CVE-2025-11339 Overview
CVE-2025-11339 is a buffer overflow vulnerability in the D-Link DI-7100G C1 router firmware up to version 20250928. The flaw resides in the sub_4BD4F8 function of /webchat/hi_block.asp, served by the jhttpd component. Attackers can manipulate the popupId argument to overflow a fixed-size buffer and corrupt adjacent memory.
The vulnerability is reachable over the network and requires low privileges. The exploit has been publicly disclosed, increasing the risk of opportunistic abuse against exposed devices. The weakness is classified under CWE-119, improper restriction of operations within the bounds of a memory buffer.
Critical Impact
A remote, authenticated attacker can trigger a buffer overflow in jhttpd through the popupId parameter, leading to memory corruption, potential code execution, and full compromise of the router.
Affected Products
- D-Link DI-7100G C1 hardware revision
- D-Link DI-7100G C1 firmware versions up to 20250928
- Deployments exposing the jhttpd web management interface
Discovery Timeline
- 2025-10-06 - CVE-2025-11339 published to NVD
- 2025-11-19 - Last updated in NVD database
Technical Details for CVE-2025-11339
Vulnerability Analysis
The flaw exists in sub_4BD4F8, a handler inside the jhttpd web server that processes requests to /webchat/hi_block.asp. The function reads the popupId request argument and copies it into a fixed-size stack or heap buffer without enforcing length checks. Supplying an oversized popupId value overruns the destination buffer and corrupts adjacent memory, including saved return addresses and control structures.
On embedded MIPS or ARM targets typical of D-Link consumer-grade gateways, such overflows often translate to arbitrary code execution. The jhttpd process generally runs with elevated privileges on the device, so a successful exploit yields full administrative control of the router.
Root Cause
The root cause is missing bounds validation on attacker-controlled input prior to a memory copy operation [CWE-119]. The handler trusts the size of the popupId argument and uses an unsafe string or memory copy primitive against a fixed-length destination buffer. No length sanitization, allocation sizing, or canary-style mitigation prevents the overrun.
Attack Vector
Exploitation requires network access to the router's web management interface and a low-privileged session on jhttpd. The attacker issues a crafted HTTP request to /webchat/hi_block.asp with an oversized popupId parameter. The malformed value overflows the target buffer inside sub_4BD4F8 and overwrites control data on the stack or heap.
Depending on memory layout and any mitigations present in the firmware, the overflow can crash the service, achieve denial of service, or be developed into a remote code execution primitive. Public disclosure of the technique lowers the effort required to weaponize the issue.
Detection Methods for CVE-2025-11339
Indicators of Compromise
- HTTP requests to /webchat/hi_block.asp containing unusually long popupId parameter values
- Repeated crashes, restarts, or watchdog resets of the jhttpd process on DI-7100G C1 devices
- Unexpected outbound connections originating from the router management plane
- New administrative accounts or modified firewall rules without authorized change tickets
Detection Strategies
- Inspect web server and reverse proxy logs for requests targeting /webchat/hi_block.asp with popupId lengths exceeding typical session identifier sizes
- Deploy network IDS signatures that flag oversized query parameters destined for D-Link management interfaces
- Correlate authentication events with subsequent crashes or anomalous CPU usage on the router
Monitoring Recommendations
- Forward router syslog and HTTP access logs to a centralized analytics platform for retention and correlation
- Alert on management-plane access from IP addresses outside an approved administrative allowlist
- Track firmware versions across the fleet and flag any DI-7100G C1 unit still running builds at or before 20250928
How to Mitigate CVE-2025-11339
Immediate Actions Required
- Restrict access to the router web management interface to trusted administrative networks only
- Disable WAN-side management on DI-7100G C1 devices until a vendor fix is applied
- Rotate administrative credentials, since exploitation requires only low privileges
- Monitor D-Link advisories at the D-Link Official Website for firmware updates addressing CVE-2025-11339
Patch Information
At the time of publication, no vendor advisory or fixed firmware build has been published for CVE-2025-11339. Track the VulDB entry #327222 and the technical write-up on Yuque for updates. Apply the official D-Link firmware update as soon as it becomes available and validate the running version after deployment.
Workarounds
- Place the router management interface behind a VPN or jump host and block direct internet exposure of jhttpd
- Apply firewall ACLs that limit HTTP and HTTPS access to the device to a small set of administrative source addresses
- Enforce strong, unique administrative passwords and disable any unused management accounts to reduce the low-privilege precondition
- Where feasible, replace end-of-support or unpatched DI-7100G C1 units with currently supported hardware
# Example: restrict router management access at an upstream firewall
# Allow only the admin subnet to reach the DI-7100G C1 web interface
iptables -A FORWARD -s 10.10.0.0/24 -d 192.0.2.1 -p tcp --dport 80 -j ACCEPT
iptables -A FORWARD -s 10.10.0.0/24 -d 192.0.2.1 -p tcp --dport 443 -j ACCEPT
iptables -A FORWARD -d 192.0.2.1 -p tcp --dport 80 -j DROP
iptables -A FORWARD -d 192.0.2.1 -p tcp --dport 443 -j DROP
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
