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

MITRE NVD CVE.ORG JSON API

Summary

CVECVE-2022-4993
StatePUBLISHED
AssignerCPANSec
Source PriorityCVE Program / NVD first with legacy fallback
Published2026-08-13 17:17:17 UTC
Updated2026-08-15 13:17:28 UTC
DescriptionHTML::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.

Risk And Classification

Primary CVSS: v3.1 9.1 CRITICAL from ADP

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N

EPSS: 0.004810000 probability, percentile 0.394300000 (date 2026-08-16)

Problem Types: CWE-470 | CWE-1336 | CWE-1336 CWE-1336 Improper Neutralization of Special Elements Used in a Template Engine | CWE-470 CWE-470 Use of Externally-Controlled Input to Select Classes or Code ('Unsafe Reflection')

VersionSourceTypeScoreSeverityVector
3.1ADPDECLARED9.1CRITICALCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N
3.1134c704f-9b21-4f2e-91b3-4a467353bcc0Secondary9.1CRITICALCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N

CVSS v3.1 Breakdown

Attack Vector
Network
Attack Complexity
Low
Privileges Required
None
User Interaction
None
Scope
Unchanged
Confidentiality
High
Integrity
High
Availability
None

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N

References

ReferenceSourceLinkTags
metacpan.org/release/GSHANK/HTML-FormHandler-0.40068/source/lib/HTML/FormH... 9b29abf9-4ab0-4765-b253-1875cd9b441e metacpan.org
security.metacpan.org/patches/H/HTML-FormHandler/0.40068/CVE-2022-4993-r2.patch 9b29abf9-4ab0-4765-b253-1875cd9b441e security.metacpan.org
github.com/gshank/html-formhandler/pull/159 9b29abf9-4ab0-4765-b253-1875cd9b441e github.com
metacpan.org/release/GSHANK/HTML-FormHandler-0.40068/source/lib/HTML/FormH... 9b29abf9-4ab0-4765-b253-1875cd9b441e metacpan.org
www.cve.org/CVERecord 9b29abf9-4ab0-4765-b253-1875cd9b441e www.cve.org
metacpan.org/release/GSHANK/HTML-FormHandler-0.40068/source/lib/HTML/FormH... 9b29abf9-4ab0-4765-b253-1875cd9b441e metacpan.org
CVE Program record CVE.ORG www.cve.org canonical
NVD vulnerability detail NVD nvd.nist.gov canonical, analysis

Additional Advisory Data

SourceTimeEvent
CNA2022-01-10T00:00:00.000ZIssue was first reported to author without a proof of concept.
CNA2024-10-27T00:00:00.000ZIssue was forwarded to CPANSec.
CNA2026-06-22T00:00:00.000ZInvestigation and development of proof of concept by CPANSec, aided by LLM tooling.
CNA2026-07-02T00:00:00.000ZIssue was again reported to author with proof of concept.
CNA2026-07-30T00:00:00.000ZAdditional analysis and development of patch by CPANSec, aided by LLM tooling.
CNA2026-08-13T00:00:00.000ZCVE-2022-4993 published

Workarounds

CNA: 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.

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