How severe is CVE-2026-46644?

No CVSS score has been assigned to CVE-2026-46644 yet. Review the advisory details and affected package list to assess your exposure.

Which packages are affected by CVE-2026-46644?

CVE-2026-46644 affects the following packages: symfony/polyfill (Packagist), symfony/polyfill-intl-idn (Packagist). Ecosystems affected: Packagist.

How do I fix CVE-2026-46644?

Update symfony/polyfill to 1.38.1 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-46644 is resolved across your whole dependency graph.

How do I detect CVE-2026-46644 in my Packagist dependencies?

Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for symfony/polyfill, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.

How do I mitigate CVE-2026-46644 if there is no patch (or I can't update yet)?

Restrict outbound requests from the affected component to an allowlist of hosts, block access to link-local and internal address ranges at the network layer, and require authentication on internal services so a forged request cannot reach them unauthenticated.

Is CVE-2026-46644 actively exploited in the wild?

No public exploit code has been indexed for CVE-2026-46644 yet. This does not mean the vulnerability cannot be exploited — absence of public exploits does not imply safety. Apply the recommended fix and use O3 Security to monitor your exposure.

What is the EPSS score for CVE-2026-46644?

CVE-2026-46644 has an EPSS (Exploit Prediction Scoring System) score of 0.5%, placing it in the 43th percentile of all CVEs. EPSS is maintained by FIRST.org and estimates the probability that a vulnerability will be exploited in the wild within the next 30 days. This score indicates relatively lower exploitation probability, though the CVSS severity should still guide your patching priority.

What type of vulnerability is CVE-2026-46644?

CVE-2026-46644 is classified as CWE-1289 (CWE-1289). This weakness type describe the underlying flaw category, which helps determine the potential impact and the right class of mitigation.

When was CVE-2026-46644 published, and has it been updated?

CVE-2026-46644 was published on July 14, 2026 and was last updated on August 12, 2026. Advisory data evolves as severity scores, affected ranges, and exploit intelligence are revised — always check the latest version of the advisory before acting.

🐘 Packagist

Not in CISA KEV

CVE-2026-46644 — polyfill

Fix: symfony/polyfill@1be936e

CVE-2026-46644 is a CWE-1289 vulnerability in symfony/polyfill. A fix is available for symfony/polyfill — see the affected versions and patch details below.

symfony/polyfill-intl-idn accepts xn-- labels whose Punycode payload decodes to ASCII-only: insecure equivalence

Also known asGHSA-2xf4-cg6j-vhgq

Published

Jul 14, 2026

Updated

Aug 12, 2026

Affected

2 pkgs

Patched

2 / 2

Exploits

None indexed

Exploitation data as of Oct 8, 2026 · OSV.dev, NVD, FIRST.org (EPSS)

Exploitation Status

No confirmed exploitation observed yet

CISA assesses this as automatable — exploitation doesn’t require manual, per-target effort, which raises the odds of mass scanning and opportunistic attacks.
CISA’s own triage has not observed active exploitation or public proof-of-concept code for this CVE as of its last assessment.

Exploitation and automatability from CISA’s SSVC triage for CVE-2026-46644.

EPSS Exploitation Probability

via FIRST.org ↗

0.5%probability of exploitation in next 30 days

Lower Risk0.00%

Lower risk than most CVEs43th percentile — riskier than 43% of all scored CVEsHighest risk

Probability of exploitation in the next 30 days, from FIRST.org EPSS.

Real-World Exposure

2 pkgs affected

🐘symfony/polyfill🐘symfony/polyfill-intl-idn

Real-time download stats are indexed for npm and PyPI packages. This vulnerability affects Packagist packages — download data is not available via public APIs for these ecosystems.

Description

symfony/polyfill-intl-idn provides a userland implementation of idn_to_utf8() and idn_to_ascii() 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 IDNA_ERROR_INVALID_ACE_LABEL. 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 IDNA_USE_STD3_RULES | IDNA_CHECK_BIDI | IDNA_CHECK_CONTEXTJ | IDNA_NONTRANSITIONAL_TO_ASCII:

Input	Polyfill output	Native `ext-intl` output
`poc.xn--kc1zs4-.com`	`poc.kc1zs4.com`	`false` (`errors=1024`)
`poc.kc1zs4.xn--`	`poc.kc1zs4.`	`false` (`errors=1024`)

Applications using the polyfill to canonicalise or compare hostnames inherit the inconsistency.

Resolution

Idn::process() now records IDNA_ERROR_INVALID_ACE_LABEL when a Punycode payload decodes to an empty string or to a string containing only ASCII code points, matching the native ext-intl behaviour and UTS #46 revision 33.

The patch for this issue is available here for branch 1.x.

Credits

Symfony would like to thank Nazy Mad for reporting the issue and Nicolas Grekas for providing the fix.

Affected Packages

2 total 2 fixed

Ecosystem	Package	Vulnerable range	Fix
🐘Packagist	`symfony/polyfill`	≥ 1.17.1&&< 1.38.1	1.38.1`composer require symfony/polyfill:^1.38.1`
🐘Packagist	`symfony/polyfill-intl-idn`	≥ 1.17.1&&< 1.38.1	1.38.1`composer require symfony/polyfill-intl-idn:^1.38.1`

Detection & mitigation playbook

Open-source dependency

Detect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for symfony/polyfill, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update symfony/polyfill to 1.38.1 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-46644 is resolved across your whole dependency graph.
Workarounds
Restrict outbound requests from the affected component to an allowlist of hosts, block access to link-local and internal address ranges at the network layer, and require authentication on internal services so a forged request cannot reach them unauthenticated.

Frequently Asked Questions

### Description `symfony/polyfill-intl-idn` provides a userland implementation of `idn_to_utf8()` and `idn_to_ascii()` 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