CVE-2026-82736 in ash
Summary
by MITRE • 09/01/2026
Incorrect Behavior Order: Validate Before Canonicalize vulnerability in ash-project ash lets an attacker store a case-insensitive string value that violates its length or match constraints.
Ash.Type.CiString.apply_constraints/2 (lib/ash/type/ci_string.ex) validated the max_length, min_length, and match constraints against the value as submitted, while the type case-folds the string (per its casing) for storage and comparison. Because validation ran before folding, an attacker can submit a value whose folded form breaks a constraint but whose original form passes: for example, against a match pattern requiring uppercase, an uppercase value that is stored lowercased persists a value the pattern rejects. The fix case-folds the value at the start of apply_constraints/2, so the constraints are checked against the form that is actually stored.
This issue affects ash: from 1.29.0-rc0 before 3.32.2.
If you want to get best quality of vulnerability data, you may have to visit VulDB.
Analysis
by VulDB Data Team • 09/01/2026
The vulnerability identified in the Ash framework represents a critical logic error within its type system, specifically affecting the CiString (Case Insensitive String) implementation. This flaw stems from an incorrect order of operations during data validation and normalization. In secure application development, it is standard practice to canonicalize or normalize input before applying constraints such as length limits, pattern matching rules, or character set restrictions. However, in versions of Ash ranging from 1.29.0-rc0 up to but not including 3.32.2, the validation logic was executed on the raw user-supplied string prior to case-folding it for storage. This sequence allows an attacker to bypass security constraints by exploiting the discrepancy between the input format and the stored format. The core technical flaw lies in the apply_constraints/2 function within lib/ash/type/ci_string.ex, which checks properties like max_length, min_length, and regex match patterns against the unmodified string rather than its case-folded equivalent.
From a security architecture perspective, this vulnerability aligns with CWE-839, which describes an incorrect order of operations where validation occurs before normalization or canonicalization. By validating the pre-normalized input, the application fails to account for how the data will actually be processed and stored internally. For instance, if a constraint requires that all strings match a specific uppercase pattern, an attacker can submit a string in lowercase that technically violates the spirit of the rule but passes the regex check because the validation logic does not yet know it will be converted to lowercase upon storage. Similarly, length constraints may be bypassed if character encoding or case conversion affects byte counts differently than expected by the validator, although the primary risk here is logical constraint evasion rather than buffer overflow. This behavior undermines data integrity and consistency guarantees that developers rely on when defining strict schemas for their resources.
The operational impact of this vulnerability allows an attacker to store values that violate business logic constraints or security policies defined in the application schema. If these constraints are used to enforce access control rules, input sanitization standards, or regulatory compliance requirements such as password complexity or identifier uniqueness, bypassing them could lead to privilege escalation, data corruption, or non-compliance with industry standards. For example, a system might reject lowercase passwords for security reasons but accept them if the validation happens before case folding, resulting in weak credentials being stored and used for authentication. This inconsistency can also be exploited in conjunction with other vulnerabilities, such as injection attacks, where the bypassed constraints allow malicious payloads to enter the database that would otherwise have been rejected by pattern matching rules designed to filter out dangerous characters or structures.
To mitigate this vulnerability, developers must upgrade the Ash framework to version 3.32.2 or later, which corrects the execution order by case-folding the value at the very beginning of the apply_constraints/2 function. This ensures that all subsequent checks are performed against the canonicalized form of the string, matching exactly what is persisted in the database. For applications unable to upgrade immediately, a temporary workaround involves implementing custom validation logic or pre-processing steps that normalize input case before it reaches the Ash type system, although this approach increases complexity and maintenance overhead. It is also advisable to review existing data stores for any records created during the vulnerable period that may violate intended constraints, as these entries could pose ongoing risks if relied upon for security decisions. Regular auditing of schema definitions against actual stored data can help identify residual inconsistencies resulting from this flaw.
This incident highlights the importance of adhering to established secure coding practices regarding input handling and validation sequences. Security frameworks like MITRE ATT&CK do not have a direct technique specifically named for this exact code-level logic error, but it falls under broader categories of application layer attacks where configuration or implementation flaws allow unauthorized data manipulation. Specifically, it relates to techniques involving improper input validation that facilitate persistence or evasion of detection mechanisms. By ensuring that normalization precedes validation, developers can prevent attackers from exploiting edge cases in string processing to bypass security controls. Maintaining up-to-date dependencies and rigorously testing type constraints with both upper and lower case inputs are essential steps in preventing similar issues in future development cycles.