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Weakness · BaseCWE-639

CWE-639: Authorization Bypass Through User-Controlled Key

Likelihood of exploit: HighBase

As of 2026-10-05, CWE-639 (Authorization Bypass Through User-Controlled Key) underlies 49 CVEs tracked by Threadlinqs, none of them in the CISA Known Exploited Vulnerabilities catalog, and is cited by 31 tracked threats. MITRE rates its likelihood of exploit as High.

CVEs
49Mapped to CWE-639
CISA KEV
0None listed yet
Critical
4CVSS v3 critical CVEs
Threats
31Tracked campaigns citing it
Likelihood
HighMITRE likelihood of exploit

Last updated:

What is CWE-639?

The system's authorization functionality does not prevent one user from gaining access to another user's data or record by modifying the key value identifying the data.

Retrieval of a user record occurs in the system based on some key value that is under user control. The key would typically identify a user-related record stored in the system and would be used to lookup that record for presentation to the user. It is likely that an attacker would have to be an authenticated user in the system. However, the authorization process would not properly check the data access operation to ensure that the authenticated user performing the operation has sufficient entitlements to perform the requested data access, hence bypassing any other authorization checks present in the system. For example, attackers can look at places where user specific data is retrieved (e.g. search screens) and determine whether the key for the item being looked up is controllable externally. The key may be a hidden field in the HTML form field, might be passed as a URL parameter or as an unencrypted cookie variable, then in each of these cases it will be possible to tamper with the key value. One manifestation of this weakness is when a system uses sequential or otherwise easily-guessable session IDs that would allow one user to easily switch to another user's session and read/modify their data.

CWE-639 is a base-level weakness in MITRE’s Common Weakness Enumeration, with a MITRE likelihood of exploit of High. Applicable platforms: Not Language-Specific.

Source: MITRE CWE (CWE-639 definition, reproduced verbatim). Counts and linkage below are Threadlinqs data.

Consequences

  • Access Control — Bypass Protection Mechanism. Access control checks for specific user data or functionality can be bypassed.
  • Access Control — Gain Privileges or Assume Identity. Horizontal escalation of privilege is possible (one user can view/modify information of another user).
  • Access Control — Gain Privileges or Assume Identity. Vertical escalation of privilege is possible if the user-controlled key is actually a flag that indicates administrator status, allowing the attacker to gain administrative access.

Source: MITRE CWE, common consequences.

How CWE-639 is exploited in the wild

Threadlinqs maps 49 CVEs to CWE-639, published between 2026-06-21 and 2026-10-03. None of them is in the CISA KEV catalog yet. By CVSS v3 severity the set splits into 4 critical, 13 high, 22 medium. The highest EPSS score in the set is 0.8% (CVE-2026-83711), the modelled probability of exploitation in the next 30 days. 31 tracked threats reference CWE-639 directly or through a CVE it covers; the most recent is “Kiteworks 9.5.1 Patches 126 Vulnerabilities Including Critical Account Takeover in Core and Email Protection Gateway (CVE-2026-102147, CVE-2026-102149)” (2026-10-02). Affected products concentrate in dromara (5), Elastic (2), FOSSBilling (2), among 35 vendors in total.

Vulnerabilities (CVEs)

Showing 40 of 49 CVEs mapped to CWE-639, CISA KEV first, then by CVSS score.

Affected vendors

Threat activity

31 tracked threats cite CWE-639; the 25 most recent are listed.

Mitigations

  • Architecture and Design: For each and every data access, ensure that the user has sufficient privilege to access the record that is being requested.
  • Architecture and Design, Implementation: Make sure that the key that is used in the lookup of a specific user's record is not controllable externally by the user or that any tampering can be detected.
  • Architecture and Design: Use encryption in order to make it more difficult to guess other legitimate values of the key or associate a digital signature with the key so that the server can verify that there has been no tampering.

Source: MITRE CWE, potential mitigations.

Detection methods (MITRE CWE)

  • Automated Static Analysis: Automated static analysis, commonly referred to as Static Application Security Testing (SAST), can find some instances of this weakness by analyzing source code (or binary/compiled code) without having to execute it. Typically, this is done by building a model of data flow and control flow, then searching for potentially-vulnerable patterns that connect "sources" (origins of input) with "sinks" (destinations where the data interacts with external components, a lower layer such as the OS, etc.)

Source: MITRE CWE, detection methods. Threadlinqs detection rules for the threats above are Blue tier and higher.