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Weakness · BaseCWE-203

CWE-203: Observable Discrepancy

Base

As of 2026-10-11, CWE-203 (Observable Discrepancy) underlies 3 CVEs tracked by Threadlinqs, none of them in the CISA Known Exploited Vulnerabilities catalog, and is cited by 4 tracked threats.

CVEs
3Mapped to CWE-203
CISA KEV
0None listed yet
Critical
0CVSS v3 critical CVEs
Threats
4Tracked campaigns citing it
Likelihood
—MITRE likelihood of exploit

Last updated:

What is CWE-203?

The product behaves differently or sends different responses under different circumstances in a way that is observable to an unauthorized actor.

CWE-203 is a base-level weakness in MITRE’s Common Weakness Enumeration. Applicable platforms: Not Language-Specific; Not Technology-Specific.

Source: MITRE CWE (CWE-203 definition, reproduced verbatim). Counts and linkage below are Threadlinqs data.

Consequences

  • Confidentiality, Access Control — Read Application Data, Bypass Protection Mechanism. An attacker can gain access to sensitive information about the system, including authentication information that may allow an attacker to gain access to the system. Other security-relevant information about the operation or internal state of the product may be revealed to an unauthorized actor, such as whether a particular operation was successful or not.
  • Confidentiality — Read Application Data. In some cases, discrepancies can be used by attackers to form a side channel. When cryptographic primitives are vulnerable to side-channel attacks, this could be used to reveal unencrypted plaintext in the worst case.

Source: MITRE CWE, common consequences.

How CWE-203 is exploited in the wild

Threadlinqs maps 3 CVEs to CWE-203, published between 2026-06-20 and 2026-09-09. None of them is in the CISA KEV catalog yet. By CVSS v3 severity the set splits into 3 medium. The highest EPSS score in the set is 0.2% (CVE-2026-87518), the modelled probability of exploitation in the next 30 days. 4 tracked threats reference CWE-203 directly or through a CVE it covers; the most recent is “Multiple Vulnerabilities in Microsoft Edge prior to 154.0.4258.53 (HK GovCERT A26-10-03)” (2026-10-02). Affected products concentrate in Capgo (2), Google (1).

Vulnerabilities (CVEs)

All 3 CVEs mapped to CWE-203, CISA KEV first, then by CVSS score.

Affected vendors

Threat activity

4 tracked threats cite CWE-203:

Mitigations

  • Architecture and Design / Separation of Privilege: Compartmentalize the system to have "safe" areas where trust boundaries can be unambiguously drawn. Do not allow sensitive data to go outside of the trust boundary and always be careful when interfacing with a compartment outside of the safe area. Ensure that appropriate compartmentalization is built into the system design, and the compartmentalization allows for and reinforces privilege separation functionality. Architects and designers should rely on the principle of least privilege to decide the appropriate time to use privileges and the time to drop privileges.
  • Implementation: Ensure that error messages only contain minimal details that are useful to the intended audience and no one else. The messages need to strike the balance between being too cryptic (which can confuse users) or being too detailed (which may reveal more than intended). The messages should not reveal the methods that were used to determine the error. Attackers can use detailed information to refine or optimize their original attack, thereby increasing their chances of success. If errors must be captured in some detail, record them in log messages, but consider what could occur if the log message

Source: MITRE CWE, potential mitigations.