CVE-2026-42876 Vulnerability Analysis & Exploit Details

CVE-2026-42876 Vulnerability Summary

CVE-2026-42876: External Secrets Operator reads information from a third-party service and automatically injects the values as Kubernetes Secrets. Prior to 2.4.1, a user who only has permission to create ExternalSecret resources can cause the operator to create a Secret that Kubernetes will automatically populate with a long-lived token for the specified service account. This effectively allows the user to impersonate any service account in the namespace without needing direct create permissions on TokenRequest or Secrets of that type. This vulnerability is fixed in 2.4.1.

CVE-2026-42876 References

External References

• https://github.com/external-secrets/external-secrets/commit/4ddd240af7fe88725d9857b9a0c198073502e288
• https://github.com/external-secrets/external-secrets/releases/tag/v2.4.1
• https://github.com/external-secrets/external-secrets/security/advisories/GHSA-fq7h-9x26-6j22

CWE Common Weakness Enumeration

CAPEC Common Attack Pattern Enumeration and Classification

• Accessing Functionality Not Properly Constrained by ACLs CAPEC-1 In applications, particularly web applications, access to functionality is mitigated by an authorization framework. This framework maps Access Control Lists (ACLs) to elements of the application's functionality; particularly URL's for web apps. In the case that the administrator failed to specify an ACL for a particular element, an attacker may be able to access it with impunity. An attacker with the ability to access functionality not properly constrained by ACLs can obtain sensitive information and possibly compromise the entire application. Such an attacker can access resources that must be available only to users at a higher privilege level, can access management sections of the application, or can run queries for data that they otherwise not supposed to.
• Cross Zone Scripting CAPEC-104 An attacker is able to cause a victim to load content into their web-browser that bypasses security zone controls and gain access to increased privileges to execute scripting code or other web objects such as unsigned ActiveX controls or applets. This is a privilege elevation attack targeted at zone-based web-browser security.
• Directory Indexing CAPEC-127 An adversary crafts a request to a target that results in the target listing/indexing the content of a directory as output. One common method of triggering directory contents as output is to construct a request containing a path that terminates in a directory name rather than a file name since many applications are configured to provide a list of the directory's contents when such a request is received. An adversary can use this to explore the directory tree on a target as well as learn the names of files. This can often end up revealing test files, backup files, temporary files, hidden files, configuration files, user accounts, script contents, as well as naming conventions, all of which can be used by an attacker to mount additional attacks.
• Subverting Environment Variable Values CAPEC-13 The adversary directly or indirectly modifies environment variables used by or controlling the target software. The adversary's goal is to cause the target software to deviate from its expected operation in a manner that benefits the adversary.
• Using Malicious Files CAPEC-17 An attack of this type exploits a system's configuration that allows an adversary to either directly access an executable file, for example through shell access; or in a possible worst case allows an adversary to upload a file and then execute it. Web servers, ftp servers, and message oriented middleware systems which have many integration points are particularly vulnerable, because both the programmers and the administrators must be in synch regarding the interfaces and the correct privileges for each interface.
• Manipulating Opaque Client-based Data Tokens CAPEC-39 In circumstances where an application holds important data client-side in tokens (cookies, URLs, data files, and so forth) that data can be manipulated. If client or server-side application components reinterpret that data as authentication tokens or data (such as store item pricing or wallet information) then even opaquely manipulating that data may bear fruit for an Attacker. In this pattern an attacker undermines the assumption that client side tokens have been adequately protected from tampering through use of encryption or obfuscation.
• Bypassing ATA Password Security CAPEC-402 An adversary exploits a weakness in ATA security on a drive to gain access to the information the drive contains without supplying the proper credentials. ATA Security is often employed to protect hard disk information from unauthorized access. The mechanism requires the user to type in a password before the BIOS is allowed access to drive contents. Some implementations of ATA security will accept the ATA command to update the password without the user having authenticated with the BIOS. This occurs because the security mechanism assumes the user has first authenticated via the BIOS prior to sending commands to the drive. Various methods exist for exploiting this flaw, the most common being installing the ATA protected drive into a system lacking ATA security features (a.k.a. hot swapping). Once the drive is installed into the new system the BIOS can be used to reset the drive password.
• Buffer Overflow via Symbolic Links CAPEC-45 This type of attack leverages the use of symbolic links to cause buffer overflows. An adversary can try to create or manipulate a symbolic link file such that its contents result in out of bounds data. When the target software processes the symbolic link file, it could potentially overflow internal buffers with insufficient bounds checking.
• Blue Boxing CAPEC-5 This type of attack against older telephone switches and trunks has been around for decades. A tone is sent by an adversary to impersonate a supervisor signal which has the effect of rerouting or usurping command of the line. While the US infrastructure proper may not contain widespread vulnerabilities to this type of attack, many companies are connected globally through call centers and business process outsourcing. These international systems may be operated in countries which have not upgraded Telco infrastructure and so are vulnerable to Blue boxing. Blue boxing is a result of failure on the part of the system to enforce strong authorization for administrative functions. While the infrastructure is different than standard current applications like web applications, there are historical lessons to be learned to upgrade the access control for administrative functions. This attack pattern is included in CAPEC for historical purposes.
• Poison Web Service Registry CAPEC-51 SOA and Web Services often use a registry to perform look up, get schema information, and metadata about services. A poisoned registry can redirect (think phishing for servers) the service requester to a malicious service provider, provide incorrect information in schema or metadata, and delete information about service provider interfaces.
• Session Credential Falsification through Prediction CAPEC-59 This attack targets predictable session ID in order to gain privileges. The attacker can predict the session ID used during a transaction to perform spoofing and session hijacking.
• Reusing Session IDs (aka Session Replay) CAPEC-60 This attack targets the reuse of valid session ID to spoof the target system in order to gain privileges. The attacker tries to reuse a stolen session ID used previously during a transaction to perform spoofing and session hijacking. Another name for this type of attack is Session Replay.
• Collect Data from Registries CAPEC-647 An adversary exploits a weakness in authorization to gather system-specific data and sensitive information within a registry (e.g., Windows Registry, Mac plist). These contain information about the system configuration, software, operating system, and security. The adversary can leverage information gathered in order to carry out further attacks.
• Key Negotiation of Bluetooth Attack (KNOB) CAPEC-668 An adversary can exploit a flaw in Bluetooth key negotiation allowing them to decrypt information sent between two devices communicating via Bluetooth. The adversary uses an Adversary in the Middle setup to modify packets sent between the two devices during the authentication process, specifically the entropy bits. Knowledge of the number of entropy bits will allow the attacker to easily decrypt information passing over the line of communication.
• Manipulating Web Input to File System Calls CAPEC-76 An attacker manipulates inputs to the target software which the target software passes to file system calls in the OS. The goal is to gain access to, and perhaps modify, areas of the file system that the target software did not intend to be accessible.
• Manipulating User-Controlled Variables CAPEC-77 This attack targets user controlled variables (DEBUG=1, PHP Globals, and So Forth). An adversary can override variables leveraging user-supplied, untrusted query variables directly used on the application server without any data sanitization. In extreme cases, the adversary can change variables controlling the business logic of the application. For instance, in languages like PHP, a number of poorly set default configurations may allow the user to override variables.
• Forceful Browsing CAPEC-87 An attacker employs forceful browsing (direct URL entry) to access portions of a website that are otherwise unreachable. Usually, a front controller or similar design pattern is employed to protect access to portions of a web application. Forceful browsing enables an attacker to access information, perform privileged operations and otherwise reach sections of the web application that have been improperly protected.

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