CVE-2026-19506 in WebUI
Summary
by MITRE • 08/19/2026
Race condition in `check.jst` in RDK-B WebUI `rdkb-2025q4-kirkstone.04.10.26` allows a remote attacker to gain unauthorized access via concurrent authentication requests that exploit shared authentication state.
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Analysis
by VulDB Data Team • 08/19/2026
The vulnerability identified within the RDK-B WebUI component, specifically in the check.jst file of version rdkb-2025q4-kirkstone.04.10.26, represents a critical race condition flaw that undermines the integrity of the authentication mechanism. This type of defect typically arises when multiple threads or processes access and manipulate shared resources concurrently without adequate synchronization primitives such as locks or atomic operations. In this specific context, the web interface relies on a shared state to track active user sessions and validate credentials during login attempts. When an attacker sends concurrent authentication requests simultaneously, they can exploit the timing window between the initial validation of credentials and the finalization of the session establishment process. This allows malicious actors to bypass standard security checks by manipulating the race condition, effectively tricking the system into granting access based on stale or inconsistent state data rather than a verified, secure login sequence.
From a technical perspective, this flaw aligns with CWE-362, which classifies concurrent execution using shared resources with improper synchronization as a distinct category of software weakness. The root cause lies in the application logic failing to enforce mutual exclusion during critical sections where authentication state is read and written. By flooding the endpoint with parallel requests, an attacker can create a scenario where one request validates successfully while another overwrites or corrupts the session token before it is properly secured. This exploitation technique does not require complex payload crafting but relies heavily on precise timing and network latency manipulation to succeed. The vulnerability highlights a fundamental design oversight in how the RDK-B WebUI handles high-concurrency scenarios, particularly in environments where multiple devices may attempt to authenticate with the gateway or router interface simultaneously.
The operational impact of this race condition is severe, as it directly facilitates unauthorized access to administrative interfaces and sensitive device configurations. Once an attacker gains entry through this method, they can escalate privileges, modify network settings, exfiltrate confidential data stored on the device, or install persistent malware backdoors. In residential broadband gateways managed by RDK-B, such compromise could lead to broader network infiltration, allowing attackers to intercept traffic from other devices connected to the same local area network. This poses significant risks to user privacy and infrastructure stability, potentially enabling man-in-the-middle attacks or denial-of-service conditions against internal services. The ability to bypass authentication entirely removes a primary defense layer, leaving downstream security controls exposed to direct exploitation by remote adversaries.
Mitigation strategies must focus on enforcing strict synchronization mechanisms within the application code responsible for handling login requests. Developers should implement atomic operations or mutex locks around any block of code that reads and updates shared authentication state variables. Additionally, implementing rate limiting at both the web server level and the application layer can reduce the effectiveness of concurrent request attacks by throttling excessive traffic from single source IP addresses. It is also advisable to adopt session management best practices such as generating unique, unpredictable session identifiers for each login attempt and invalidating previous tokens immediately upon successful authentication. Regular security audits focusing on concurrency issues and race conditions are essential to identify similar flaws in other parts of the web interface before they can be exploited in production environments.
This vulnerability is categorized under MITRE ATT&CK technique T1078, which covers Valid Accounts, specifically noting how attackers leverage legitimate credentials or bypass authentication mechanisms to gain initial access. The exploitation method also relates to CWE-362 and potentially CWE-490 if the system relies on trust in network-level indicators rather than robust application-layer validation. Addressing this issue requires a comprehensive review of the check.jst logic and associated backend handlers to ensure that state transitions are atomic and immune to timing-based attacks. Organizations deploying RDK-B based devices should prioritize applying vendor-provided patches or implementing compensating controls such as web application firewalls configured to detect and block suspicious patterns of concurrent authentication attempts until the underlying code defect is resolved.