CVE-2026-19611 in WildFly
Summary
by MITRE • 08/20/2026
A flaw was found in WildFly Elytron. Password hashing and verification normalize input with Unicode NFKC, which can collapse fullwidth characters to ASCII equivalents. A remote attacker can more easily guess affected passwords by using an ASCII-only dictionary against accounts whose passwords were intended to include those non-ASCII characters, leading to unauthorized access.
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Analysis
by VulDB Data Team • 08/20/2026
The vulnerability identified in WildFly Elytron represents a critical authentication bypass mechanism rooted in improper handling of Unicode normalization during password processing operations. Specifically, the flaw involves the application of Unicode Normalization Form Compatibility Composition (NFKC) to user-supplied passwords prior to hashing and verification. This standard normalization process is designed to ensure consistent representation of characters across different systems by mapping compatibility characters to their canonical equivalents. However, in this specific implementation context, NFKC normalization aggressively collapses fullwidth variants of Latin letters into their standard ASCII counterparts. For instance, a password containing the fullwidth character for 'a' (U+FF41) is normalized to the standard lowercase 'a' (U+0061). While this behavior may be intended to support internationalization and cross-platform consistency in some contexts, it inadvertently introduces a significant security weakness by reducing the effective entropy of passwords that rely on non-ASCII characters for complexity.
The operational impact of this flaw is substantial because it effectively nullifies the additional security provided by using fullwidth or other Unicode variants as part of password complexity requirements. Attackers conducting brute-force or dictionary-based attacks can now utilize standard ASCII-only wordlists to target accounts where administrators or users believed they had enhanced their security posture by including non-ASCII characters in their passwords. Since the system normalizes these inputs before comparison, a guess using an ASCII character will match a stored hash derived from its fullwidth equivalent. This significantly lowers the computational cost and time required for successful credential guessing attacks, particularly against accounts that do not enforce strict length or complexity policies beyond basic Unicode inclusion. The vulnerability essentially creates a false sense of security, leading to unauthorized access through simplified attack vectors that exploit this normalization discrepancy.
From a classification perspective, this issue aligns with CWE-757: Selection of Less-Secure Algorithm During Encryption Key Generation and Cryptographic Operations, as it involves the selection of a normalization algorithm that weakens the cryptographic strength of password storage by reducing character set diversity. It also relates to CWE-284: Improper Access Control, specifically in how authentication mechanisms fail to strictly enforce input integrity regarding expected character sets. In terms of adversary tactics, this vulnerability facilitates Credential Stuffing and Brute Force attacks as described in MITRE ATT&CK technique T1110. The ability to map non-standard inputs to standard ASCII equivalents allows attackers to bypass defenses that might otherwise detect or rate-limit unusual Unicode-based login attempts, thereby streamlining the path to initial compromise.
Mitigation strategies for this vulnerability require a multi-layered approach focusing on input validation and algorithmic configuration. Administrators should immediately apply vendor-provided patches or updates that address the normalization behavior in WildFly Elytron versions affected by this flaw. In environments where patching is not immediately feasible, implementing strict password policies at the application level can help mitigate risk. This includes enforcing minimum length requirements to compensate for reduced character set entropy and potentially restricting allowed characters to ASCII-only sets if internationalization support is not strictly required for specific user groups. Additionally, enabling multi-factor authentication provides a robust secondary layer of defense that remains effective regardless of password normalization flaws. Regular auditing of authentication logs can also help detect increased attempts from single sources attempting various Unicode-to-ASCII variations, allowing for proactive blocking before successful unauthorized access occurs.