Description
HTML::FormHandler versions through 0.40068 for Perl allow attacker selected method dispatch and resource exhaustion because _apply_actions and add_error use error message text built from request data as a Locale::Maketext bracket notation template.

add_error hands its first argument to the language handle as the Locale::Maketext message key, and the default handle's lexicon sets `_AUTO`, so a string that is not a lexicon entry is compiled as a bracket notation template instead of being looked up. In a bracket group the first token names a method called on the language handle and the remaining tokens are its arguments.

Three kinds of text the library did not author reach that position. _apply_actions installs a `$SIG{__WARN__}` handler that stores the warning text in `$error_message`, and a captured warning survives a successful action, so a field carrying a numeric transform turns `Argument "[sprintf,%50000000d,0]" isn't numeric` into the template; a warning quotes the submitted value verbatim, so the group is well formed and dispatches. `$error_message ||= $tobj->validate($new_value)` takes a type constraint's own failure message, which renders the rejected value through a partial dumper in bracket and comma form (Devel::PartialDump when Moose can load it, Type::Tiny's own dumper always), so a field with `apply => [ Str ]` given a parameter sent more than once, which arrives as an array, gets `Reference ["a","b"] did not pass type constraint "Str"` as its template, from a request that carries no bracket character of its own. A coercion or transform exception reaches it the same way. Beyond those, a validator whose message contains the field value puts that value in the template directly, and add_error replaces the message list with the contents of an arrayref first argument (`@message = @{$message[0]} if ref $message[0] eq 'ARRAY'`), so a value arriving as an array fills the argument slots from the same request as well.

A malformed group such as `[0]` makes the compile croak, and HTML::FormHandler::I18N::maketext and add_error each re-raise that as a die, so process() throws. A well formed group naming sprintf reaches CORE::sprintf with an attacker chosen field width. Any caller that applies a type constraint or a transform to an untrusted field, or whose validator passes an untrusted field value to add_error, can be made to throw an unhandled exception out of process(), or to allocate an arbitrary amount of memory in one request, and an application whose language handle subclass defines side effecting public methods makes those callable with attacker chosen arguments. The dumped type constraint message is bounded to the exception, because both dumpers quote non-numeric elements so the method slot is never an attacker chosen name. The built-in messages pass fixed templates with the value in an argument slot, where it stays inert, and the built-in field types attach explicit message callbacks, so neither is affected.
Published: 2026-08-13
Score: 9.1 Critical
EPSS: < 1% Very Low
KEV: No
Impact: n/a
Action: n/a
AI Analysis

Impact

The vulnerability arises from the way the library treats error message text built from request data as a Locale::Maketext bracket‑notation template, a misuse that falls under CWE‑470 (Improper Control of Generation of Code) and CWE‑1336 (Resource Exhaustion via Uncontrolled Input). When _apply_actions or add_error receive user‑supplied content, the text acts as a template; if the template is well‑formed, a method name in the first token is dispatched on the language handle, and the following tokens become arguments. An attacker can craft form data that contains a bracket group such as "[sprintf,1000000,0]" or a value that triggers a warning, thereby forcing the code to call arbitrary methods, allocate large amounts of memory, or raise unhandled exceptions. The impact is a high‑severity denial of service from memory exhaustion, and if the language handle implements side‑effecting public methods, a potential for arbitrary code execution.

Affected Systems

All systems that incorporate Perl’s HTML::FormHandler module of version 0.40068 or earlier are affected. This includes any web application or script that loads the module, regardless of the vendor or the host operating system.

Risk and Exploitability

The CVSS score of 9.1 indicates high severity. The vulnerability can be exploited by submitting specially crafted input to a form handled by the affected module. Attackers can trigger unhandled exceptions or consume large amounts of memory by leveraging improper template interpretation. The lack of an official fixed release means the flaw remains exploitable until the patch is applied or the module is upgraded. Because the vulnerability does not require elevated privileges or local access, it is considered high risk for any deployed application using the affected version of the module. Based on the description, it is inferred that the vulnerability imposes a high risk due to potential denial of service and code execution.

Generated by OpenCVE AI on August 14, 2026 at 13:51 UTC.

Remediation

Vendor Workaround

No fixed release is available. Apply the patch, which escapes the bracket notation metacharacters in the trapped warning, the type constraint message and the coercion or transform exception before they are used as a template, and in element 0 of an arrayref first argument. A message an application builds from a field value cannot be told apart from a template inside the library: pass a fixed template to add_error and supply the value as an argument, as the built-in messages do (`$field->add_error('[_1] not allowed', $field->value)`), so the value lands in an inert argument slot. Setting an allowlist on the language handle bounds the methods bracket notation can reach.

OpenCVE Recommended Actions

  • Apply the supplied patch that escapes bracket‑notation metacharacters in warnings, type‑constraint messages, and coercion exceptions before they are used as templates.
  • If the patch cannot be applied, enforce a fixed error template and pass user input as an argument, for example $field->add_error('[_1] not allowed', $value).
  • Configure the language handle to allowlist only safe methods for bracket‑notation dispatch, preventing arbitrary method invocation.
  • Upgrade to a newer release of HTML::FormHandler that contains the fix once it becomes available.

Generated by OpenCVE AI on August 14, 2026 at 13:51 UTC.

Tracking

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Advisories

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History

Sat, 15 Aug 2026 12:30:00 +0000

Type Values Removed Values Added
References

Fri, 14 Aug 2026 13:00:00 +0000

Type Values Removed Values Added
First Time appeared Gshank
Gshank html::formhandler
Vendors & Products Gshank
Gshank html::formhandler

Fri, 14 Aug 2026 12:30:00 +0000

Type Values Removed Values Added
Metrics cvssV3_1

{'score': 9.1, 'vector': 'CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N'}

ssvc

{'options': {'Automatable': 'yes', 'Exploitation': 'none', 'Technical Impact': 'total'}, 'version': '2.0.3'}

Thu, 13 Aug 2026 16:45:00 +0000

Type Values Removed Values Added
Description HTML::FormHandler versions through 0.40068 for Perl allow attacker selected method dispatch and resource exhaustion because _apply_actions and add_error use error message text built from request data as a Locale::Maketext bracket notation template. add_error hands its first argument to the language handle as the Locale::Maketext message key, and the default handle's lexicon sets `_AUTO`, so a string that is not a lexicon entry is compiled as a bracket notation template instead of being looked up. In a bracket group the first token names a method called on the language handle and the remaining tokens are its arguments. Three kinds of text the library did not author reach that position. _apply_actions installs a `$SIG{__WARN__}` handler that stores the warning text in `$error_message`, and a captured warning survives a successful action, so a field carrying a numeric transform turns `Argument "[sprintf,%50000000d,0]" isn't numeric` into the template; a warning quotes the submitted value verbatim, so the group is well formed and dispatches. `$error_message ||= $tobj->validate($new_value)` takes a type constraint's own failure message, which renders the rejected value through a partial dumper in bracket and comma form (Devel::PartialDump when Moose can load it, Type::Tiny's own dumper always), so a field with `apply => [ Str ]` given a parameter sent more than once, which arrives as an array, gets `Reference ["a","b"] did not pass type constraint "Str"` as its template, from a request that carries no bracket character of its own. A coercion or transform exception reaches it the same way. Beyond those, a validator whose message contains the field value puts that value in the template directly, and add_error replaces the message list with the contents of an arrayref first argument (`@message = @{$message[0]} if ref $message[0] eq 'ARRAY'`), so a value arriving as an array fills the argument slots from the same request as well. A malformed group such as `[0]` makes the compile croak, and HTML::FormHandler::I18N::maketext and add_error each re-raise that as a die, so process() throws. A well formed group naming sprintf reaches CORE::sprintf with an attacker chosen field width. Any caller that applies a type constraint or a transform to an untrusted field, or whose validator passes an untrusted field value to add_error, can be made to throw an unhandled exception out of process(), or to allocate an arbitrary amount of memory in one request, and an application whose language handle subclass defines side effecting public methods makes those callable with attacker chosen arguments. The dumped type constraint message is bounded to the exception, because both dumpers quote non-numeric elements so the method slot is never an attacker chosen name. The built-in messages pass fixed templates with the value in an argument slot, where it stays inert, and the built-in field types attach explicit message callbacks, so neither is affected.
Title HTML::FormHandler versions through 0.40068 for Perl allow attacker selected method dispatch and resource exhaustion because _apply_actions and add_error use error message text built from request data as a Locale::Maketext bracket notation template
Weaknesses CWE-1336
CWE-470
References

Subscriptions

Gshank Html::formhandler
cve-icon MITRE

Status: PUBLISHED

Assigner: CPANSec

Published:

Updated: 2026-08-15T12:13:44.455Z

Reserved: 2026-06-23T17:33:58.500Z

Link: CVE-2022-4993

cve-icon Vulnrichment

Updated: 2026-08-14T11:14:00.368Z

cve-icon NVD

Status : Deferred

Published: 2026-08-13T17:17:17.780

Modified: 2026-08-26T16:51:19.490

Link: CVE-2022-4993

cve-icon Redhat

No data.

cve-icon OpenCVE Enrichment

Updated: 2026-08-14T14:00:05Z

Weaknesses
  • CWE-1336

    Improper Neutralization of Special Elements Used in a Template Engine

  • CWE-470

    Use of Externally-Controlled Input to Select Classes or Code ('Unsafe Reflection')