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CVE-2026-46644

Vulnerability in symfony/polyfill (CVE-2026-46644)

Summary

Vulnerability in symfony/polyfill (CVE-2026-46644). Risk of unauthorized operations or information disclosure. Exploitable via intl. Mitigation: upgrade to 1.38.1 or later.

Original description

The description as published by the source.

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-…

Source: GitHub Security Advisories (Global) NVD GitHub Advisory

Auto-generated summary

Assembled by SecPulse from the source data (CVSS, CWE, affected versions) using templates — no AI involved. Check the original description and references below for exact details.

A vulnerability tracked as CVE-2026-46644 has been found in symfony/polyfill.
Attackers can target a specific entry point like intl over the network to misuse the product.
Risk of unauthorized operations or information disclosure.
What to do: upgrade symfony/polyfill to 1.38.1 or later.
If unsure, ask your IT team or search "symfony/polyfill CVE-2026-46644" on the vendor's site.

CVE-2026-46644 (symfony/polyfill) — CWE-1289
Attack surface: intl / IDNA_ERROR_INVALID_ACE_LABEL / poc.kc1zs4.com / false
Patched: 1.38.1 — apply immediately
Plan: 1) Audit SBOM/dependencies, 2) Stage→prod upgrade, 3) Add WAF/proxy monitoring on affected endpoints, 4) Hunt IOCs in logs.
Refs: see the GHSA / vendor advisory / patched release linked on this page.

❓ What is the problem

A vulnerability (CWE-1289) exists in symfony/polyfill. Attackers reach the vulnerable code path via intl.

📍 Affected scope

Check the vendor advisory for the affected versions of symfony/polyfill. Attack surface: intl / IDNA_ERROR_INVALID_ACE_LABEL / poc.kc1zs4.com / false.

🔥 Severity

Severity: ?. Risk of unauthorized operations or information disclosure.

🔧 How to fix

Update to 1.38.1.

🛡️ Workaround

Until the patch is applied: disable the affected feature, apply WAF rules, or restrict access via network ACLs.

🔍 Detection

Search webserver/proxy logs for unusual request patterns matching this CVE's known IOCs. Run grep -r 'symfony/polyfill' . against your dependency files (package-lock.json, requirements.txt, go.sum) to find affected services.

Response actions

Concrete steps and command examples for SOC/SRE teams to execute in order

  1. 1
    Identify exposure identify 
    grep -r 'symfony/polyfill' . | grep -v node_modules

    リポジトリと本番環境の依存ファイル (package-lock.json / requirements.txt / go.sum / Gemfile.lock 等) で symfony/polyfill を grep し、稼働しているサービス・バージョンを把握する。

  2. 2
    Apply patch patch 
    Upgrade symfony/polyfill to 1.38.1

    ステージング環境で 1.38.1 に上げて回帰テスト → 本番反映。回帰テストはアプリの主要ハッピーパスを含めること。

  3. 3
    Post-deployment verification verify 
    Confirm patched version is live in production

    パッチ適用後、ステージングで PoC または同等の悪用パターンを再現して脆弱性が閉じたことを確認。本番ではアクセスログ・WAF でアラート再発が無いか継続監視。

Affected packages

composer symfony/polyfill
[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"1.38.1"}]}]
composer symfony/polyfill-intl-idn
[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"1.38.1"}]}]
Packagist symfony/polyfill
[{"type":"ECOSYSTEM","events":[{"introduced":"1.17.1"},{"fixed":"1.38.1"}]}]
Packagist symfony/polyfill-intl-idn
[{"type":"ECOSYSTEM","events":[{"introduced":"1.17.1"},{"fixed":"1.38.1"}]}]

Fix status by distribution

Fixed packages published by each distribution for this CVE

References

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