CVE-2026-46644 json
symfony/polyfill-intl-idn accepts xn-- labels whose Punycode payload decodes to ASCII-only: insecure equivalence
published 2026-05-28 5 mo ago modified 2026-09-10 1 mo ago also GHSA-2xf4-cg6j-vhgq , EUVD-2026-44537
- cvss
- 6.9
- version 4.0, CNA
- cisa kev
- Not listed
- not in CISA's catalog
- epss
- 0.5%
- EPSS 0.5% chance of exploitation in 30 days, percentile 45%
- public exploits
- 0
- none known
Summary
Symfony Polyfill backports PHP features and provides compatibility layers for extensions and functions. From 1.17.1 until 1.38.1, symfony/polyfill-intl-idn accepts xn-- labels whose Punycode payload is empty or decodes to ASCII-only code points because Idn::process() does not enforce the UTS #46 revision 33 requirement that decoded ACE labels contain at least one non-ASCII code point. Originally unequal domain names can be regarded as equal, which can lead to blacklist bypassing, inconsistent URL parsing, and server-side request forgery in applications using the polyfill to canonicalise or compare hostnames. This issue is fixed in version 1.38.1.
Patch / fix
- packagist symfony/polyfill 1.38.1
- packagist symfony/polyfill-intl-idn 1.38.1
- php-symfony-polyfill Debian 14 1.38.1-1
debian advisories DEBIAN-CVE-2026-46644
CISA SSVC
- Exploitation
- none
- Automatable
- yes
- Technical impact
- partial
- Assessed
- 3 mo ago
Exploit prediction
0.54% chance of exploitation in the next 30 days, higher than 45% of all scored CVEs (FIRST EPSS, 2026-11-08).
CVSS scores
| assigned by | version | score | vector |
|---|---|---|---|
| CNA | 4.0 | 6.9 | CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:L/VA:N/SC:L/SI:L/SA:N |
| CNA | 4.0 | 6.9 | CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:L/VA:N/SC:L/SI:L/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X |
Affected packages
| ecosystem | package | affected | fixed in |
|---|---|---|---|
| packagist | symfony/polyfill | >=1.17.1, <1.38.1 |
1.38.1 |
| packagist | symfony/polyfill-intl-idn | >=1.17.1, <1.38.1 |
1.38.1 |
Affected products
- symfony polyfill
- symfony polyfill-intl-idn
Classification
- Weakness
-
- CWE-1289 Improper Validation of Unsafe Equivalence in Input
References
-
github.com
/symfony/polyfill/commit/1be936e2491ccebe152bd736dfc91eb1422c8bec
web
-
github.com
/symfony/polyfill/security/advisories/GHSA-2xf4-cg6j-vhgq
web
- github.com /symfony/polyfill/releases/tag/v1.38.1
-
github.com
/FriendsOfPHP/security-advisories/blob/master/symfony/polyfill-intl-idn/CVE-2026-46644.yaml
web
-
github.com
/FriendsOfPHP/security-advisories/blob/master/symfony/polyfill/CVE-2026-46644.yaml
web
-
github.com
/symfony/polyfill
package
-
symfony.com
/cve-2026-46644
web
Sources
- CVE List CVE-2026-46644
- GitHub Advisory GHSA-2xf4-cg6j-vhgq
- NVD CVE-2026-46644
Fencer Vulns keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.