CVE-2026-118995 in CallBackery
Summary
by MITRE • 10/30/2026
CallBackery versions before 0.62.0 for Perl accept unintended values in form fields checked by createRxValidator.
createRxValidator() is documented to anchor the supplied pattern at both ends, but builds /^${rx}$/ without grouping the pattern. An alternation such as yes|no then accepts any value starting with yes or ending with no, and $ also accepts a value with one trailing newline.
An authenticated user can submit values the pattern was meant to reject, which an application may then write into generated configuration files.
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Analysis
by VulDB Data Team • 10/30/2026
The vulnerability identified in CallBackery versions prior to 0.62.0 represents a critical input validation flaw rooted in improper regex construction within the createRxValidator function. This component is designed to enforce strict constraints on form field inputs by anchoring regular expression patterns at both the beginning and end of the string, thereby ensuring that user-supplied data matches the expected format exactly without allowing partial or extended matches. However, the implementation fails to properly group the supplied pattern before applying anchors. Specifically, the function constructs the validation regex as /^${rx}$/ rather than /^(?:${rx})$/. This subtle but significant deviation from secure coding practices fundamentally alters how the regular expression engine interprets alternation operators and end-of-string assertions within user-provided patterns.
When a developer supplies an alternating pattern such as yes|no to this validator, the lack of grouping causes the anchors to apply only to the first alternative or behave unpredictably depending on regex engine specifics. In practice, this results in the validation accepting any string that starts with yes or ends with no, rather than strictly matching either yes or no. Furthermore, the end anchor $ is known to match a newline character at the very end of some strings before the actual end-of-string boundary, allowing inputs containing trailing newlines to bypass the intended restriction. This behavior creates a discrepancy between the documented security expectations and the actual runtime validation logic, effectively weakening the integrity checks applied to user input.
The operational impact of this vulnerability is substantial for applications relying on CallBackery to generate configuration files or system settings based on form submissions. An authenticated attacker can exploit this flaw by submitting values that were explicitly intended to be rejected by the application's business logic. Because these invalid inputs pass validation, they are subsequently written into generated configuration files without error. This can lead to misconfiguration of critical services, injection of malicious parameters, or corruption of system state depending on how the downstream processes interpret the malformed input. The ability to bypass expected constraints undermines the principle of least privilege and data integrity within the application environment.
From a classification perspective, this vulnerability aligns with CWE-20 Improper Input Validation, as the software fails to adequately verify that user-supplied input conforms to required specifications before processing it. Additionally, because the flaw allows an authenticated actor to manipulate configuration files through crafted inputs, it relates to CWE-94 Improper Control of Generation of Code or Command, specifically code injection via configuration file manipulation if those configurations are executed by a system process. In terms of adversary tactics, this exploitation vector corresponds to ATT&CK technique T1505 Server Software Component Injection, where attackers leverage vulnerable components to inject malicious content into server-side applications for persistence or further compromise.
Mitigation strategies must focus on correcting the regular expression construction logic within the createRxValidator function. The primary fix involves wrapping the user-supplied pattern in a non-capturing group before applying anchors, ensuring that /^ and $ delimiters apply to the entire logical unit of the regex rather than just its first component. Developers should also consider using strict mode or explicit end-of-string assertions such as \z instead of $ where appropriate to prevent newline matching issues. Beyond code fixes, organizations should implement comprehensive input validation layers at multiple points in the application stack and conduct regular security audits focusing on dynamic content generation and configuration management processes to detect similar patterns early.