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Weakness · BaseCWE-807

CWE-807: Reliance on Untrusted Inputs in a Security Decision

Likelihood of exploit: HighKEV-linkedBase

As of 2026-10-05, CWE-807 (Reliance on Untrusted Inputs in a Security Decision) underlies 5 CVEs tracked by Threadlinqs, 3 of them in the CISA Known Exploited Vulnerabilities catalog, and is cited by 18 tracked threats. MITRE rates its likelihood of exploit as High.

CVEs
5Mapped to CWE-807
CISA KEV
3Exploited in the wild
Critical
1CVSS v3 critical CVEs
Threats
18Tracked campaigns citing it
Likelihood
HighMITRE likelihood of exploit

Last updated:

What is CWE-807?

The product uses a protection mechanism that relies on the existence or values of an input, but the input can be modified by an untrusted actor in a way that bypasses the protection mechanism.

Developers may assume that inputs such as cookies, environment variables, and hidden form fields cannot be modified. However, an attacker could change these inputs using customized clients or other attacks. This change might not be detected. When security decisions such as authentication and authorization are made based on the values of these inputs, attackers can bypass the security of the software. Without sufficient encryption, integrity checking, or other mechanism, any input that originates from an outsider cannot be trusted.

CWE-807 is a base-level weakness in MITRE’s Common Weakness Enumeration, with a MITRE likelihood of exploit of High. Applicable platforms: Language: Not Language-Specific; Technology: Not Technology-Specific; Technology: Web Based; Technology: Web Server.

Source: MITRE CWE (CWE-807 definition, reproduced verbatim). Counts and linkage below are Threadlinqs data.

Consequences

  • Confidentiality, Access Control, Availability, Other — Bypass Protection Mechanism, Gain Privileges or Assume Identity, Varies by Context. Attackers can bypass the security decision to access whatever is being protected. The consequences will depend on the associated functionality, but they can range from granting additional privileges to untrusted users to bypassing important security checks. Ultimately, this weakness may lead to exposure or modification of sensitive data, system crash, or execution of arbitrary code.

Source: MITRE CWE, common consequences.

How CWE-807 is exploited in the wild

Threadlinqs maps 5 CVEs to CWE-807, published between 2026-01-26 and 2026-09-08. 3 are listed in CISA’s Known Exploited Vulnerabilities catalog, the authoritative record of exploitation in the wild. By CVSS v3 severity the set splits into 1 critical, 3 high, 1 medium. The highest EPSS score in the set is 42.6% (CVE-2026-34486), the modelled probability of exploitation in the next 30 days. 18 tracked threats reference CWE-807 directly or through a CVE it covers; the most recent is “DeepSeek Harness Authentication Bypass Lets Sandboxed AI Agents Escape via Single Command (CVE-2026-82533)” (2026-09-09). Affected products concentrate in Microsoft (2), Apache Software Foundation (1), DeepSeek (1), among 4 vendors in total.

Vulnerabilities (CVEs)

All 5 CVEs mapped to CWE-807, CISA KEV first, then by CVSS score.

  • CVE-2026-21509 — CISA KEV · CVSS 7.8 high · EPSS 7.4% · published 2026-01-26
  • CVE-2026-21514 — CISA KEV · CVSS 7.8 high · EPSS 4.2% · published 2026-02-10
  • CVE-2026-34486 — CISA KEV · CVSS 7.5 high · EPSS 42.6% · published 2026-04-09
  • CVE-2026-82533 — CVSS 9.6 critical · EPSS 0.4% · published 2026-09-08
  • CVE-2026-64934 — CVSS 4.3 medium · EPSS 0.1% · published 2026-08-11

Affected vendors

Threat activity

18 tracked threats cite CWE-807:

Mitigations

  • Architecture and Design / Attack Surface Reduction: Store state information and sensitive data on the server side only. Ensure that the system definitively and unambiguously keeps track of its own state and user state and has rules defined for legitimate state transitions. Do not allow any application user to affect state directly in any way other than through legitimate actions leading to state transitions. If information must be stored on the client, do not do so without encryption and integrity checking, or otherwise having a mechanism on the server side to catch tampering. Use a message authentication code (MAC) algorithm, such as Hash Message Authentication Code (HMAC) [REF-529]. Apply this against the state or sensitive data that has…
  • Architecture and Design / Libraries or Frameworks: Use a vetted library or framework that does not allow this weakness to occur or provides constructs that make this weakness easier to avoid. With a stateless protocol such as HTTP, use a framework that maintains the state for you. Examples include ASP.NET View State [REF-756] and the OWASP ESAPI Session Management feature [REF-45]. Be careful of language features that provide state support, since these might be provided as a convenience to the programmer and may not be considering security.
  • Architecture and Design: For any security checks that are performed on the client side, ensure that these checks are duplicated on the server side, in order to avoid CWE-602. Attackers can bypass the client-side checks by modifying values after the checks have been performed, or by changing the client to remove the client-side checks entirely. Then, these modified values would be submitted to the server.
  • Operation, Implementation / Environment Hardening: When using PHP, configure the application so that it does not use register_globals. During implementation, develop the application so that it does not rely on this feature, but be wary of implementing a register_globals emulation that is subject to weaknesses such as CWE-95, CWE-621, and similar issues.
  • Architecture and Design, Implementation / Attack Surface Reduction: Understand all the potential areas where untrusted inputs can enter your software: parameters or arguments, cookies, anything read from the network, environment variables, reverse DNS lookups, query results, request headers, URL components, e-mail, files, filenames, databases, and any external systems that provide data to the application. Remember that such inputs may be obtained indirectly through API calls. Identify all inputs that are used for security decisions and determine if you can modify the design so that you do not have to rely on submitted inputs at all. For example, you may be able to keep critical information about the user's session on the server side instead of recording it…

Source: MITRE CWE, potential mitigations.

Detection methods (MITRE CWE)

  • Manual Static Analysis (effectiveness: High): Since this weakness does not typically appear frequently within a single software package, manual white box techniques may be able to provide sufficient code coverage and reduction of false positives if all potentially-vulnerable operations can be assessed within limited time constraints.
  • Automated Static Analysis - Binary or Bytecode (effectiveness: SOAR Partial): According to SOAR [REF-1479], the following detection techniques may be useful: Cost effective for partial coverage: Bytecode Weakness Analysis - including disassembler + source code weakness analysis Binary Weakness Analysis - including disassembler + source code weakness analysis
  • Manual Static Analysis - Binary or Bytecode (effectiveness: SOAR Partial): According to SOAR [REF-1479], the following detection techniques may be useful: Cost effective for partial coverage: Binary / Bytecode disassembler - then use manual analysis for vulnerabilities & anomalies
  • Dynamic Analysis with Automated Results Interpretation (effectiveness: SOAR Partial): According to SOAR [REF-1479], the following detection techniques may be useful: Cost effective for partial coverage: Web Application Scanner Web Services Scanner Database Scanners
  • Dynamic Analysis with Manual Results Interpretation (effectiveness: SOAR Partial): According to SOAR [REF-1479], the following detection techniques may be useful: Cost effective for partial coverage: Fuzz Tester Framework-based Fuzzer Monitored Virtual Environment - run potentially malicious code in sandbox / wrapper / virtual machine, see if it does anything suspicious
  • Manual Static Analysis - Source Code (effectiveness: High): According to SOAR [REF-1479], the following detection techniques may be useful: Highly cost effective: Manual Source Code Review (not inspections)
  • Automated Static Analysis - Source Code (effectiveness: SOAR Partial): According to SOAR [REF-1479], the following detection techniques may be useful: Cost effective for partial coverage: Source code Weakness Analyzer Context-configured Source Code Weakness Analyzer
  • Architecture or Design Review (effectiveness: High): According to SOAR [REF-1479], the following detection techniques may be useful: Highly cost effective: Inspection (IEEE 1028 standard) (can apply to requirements, design, source code, etc.) Formal Methods / Correct-By-Construction Cost effective for partial coverage: Attack Modeling

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