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Low, CVSS 2.7

symfony/polyfill-intl-idn: xn-- labels with ASCII-only Punycode payloads are treated as equivalent to their decoded form

CVE-2026-46644GHSA-2xf4-cg6j-vhgq

What to do

Vendor fix available. Upgrade each affected package to the fixed version on its release line (symfony/polyfill 1.38.1; symfony/polyfill-intl-idn 1.38.1), redeploy, then verify what is actually installed.

This page has no inventory attached, so it cannot say whether you are affected. A vendor fix is not proof that your deployment is fixed.

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Affected packages

Sources

Severity and exploitation
Exploitation
No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.
CVSS 4.0
2.7 · CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:L/VA:N/SC:N/SI:L/SA:N/E:U · score source
EPSS
  • CVE-2026-46644: 0.54% estimated exploitation activity in the next 30 days; percentile 45.34 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.
Source description

As published by the source; long descriptions are shortened.

Description symfony/polyfill-intl-idn provides a userland implementation of idntoutf8() and idntoascii() for runtimes that lack the intl extension. Its Idn::process() method decodes labels prefixed with xn-- using Punycode but never enforces the validity criterion added in UTS #46 revision 33 Section 4 step 4.1.2: after a successful Punycode decode, the result must contain at least one non-ASCII code point. As a consequence, xn-- labels whose Punycode payload is empty (xn--) or decodes to a string made of only ASCII code points (e.g. xn--kc1zs4-) are accepted by the polyfill while PHP's native ext-intl rejects them with IDNAERRORINVALIDACELABEL. Originally unequal domain names are therefore regarded as equal, which can lead to blacklist bypassing, inconsistent URL parsing and server-side request forgery (similar to CVE-2024-12224). Example with IDNAUSESTD3RULES | IDNACHECKBIDI | IDNACHECKCONTEXTJ | IDNANONTRANSITIONALTOASCII: | Input | Polyfill output | Native ext-intl output | | ---…

Dates and revisions
Published by the source
Last modified by the source
Source last checked
  1. Revision 1 · created ·

    Published from ghsa record GHSA-2xf4-cg6j-vhgq

Agent brief

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# Patch Next advisory brief: CVE-2026-46644

Advisory: symfony/polyfill-intl-idn: xn-- labels with ASCII-only Punycode payloads are treated as equivalent to their decoded form
IDs: CVE-2026-46644, GHSA-2xf4-cg6j-vhgq
Record: https://patchnext.com/advisories/cve-2026-46644 (revision 1, source checked 26 Oct 2026, 14:48 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: Low (CVSS 2.7)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: symfony/polyfill 1.38.1; symfony/polyfill-intl-idn 1.38.1. A vendor fix does not mean a deployment is fixed.

## Affected components
- Packagist symfony/polyfill: affected >= 1.17.1, < 1.38.1; fixed in 1.38.1
- Packagist symfony/polyfill-intl-idn: affected >= 1.17.1, < 1.38.1; fixed in 1.38.1

## Suggested inspection (read-only)
- Packagist symfony/polyfill: check the installed version with your package manager.
- Packagist symfony/polyfill-intl-idn: check the installed version with your package manager.

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on symfony/polyfill, symfony/polyfill-intl-idn.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://github.com/advisories/GHSA-2xf4-cg6j-vhgq (GitHub-reviewed advisory GHSA-2xf4-cg6j-vhgq lists affected ranges: Packagist symfony/polyfill >=1.17.1 =1.17.1 <1.38.1)

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