Description
Nu Html Checker (validator.nu) contains a restriction bypass that allows remote attackers to make the server perform arbitrary HTTP/HTTPS requests to internal resources, including localhost services. While the validator implements hostname-based protections to block direct access to localhost and 127.0.0.1, these controls can be bypassed using DNS rebinding techniques or domains that resolve to loopback addresses.This issue affects The Nu Html Checker (vnu): latest (commit 23f090a11bab8d0d4e698f1ffc197a4fe226a9cd).
Affected products
| Vendor | Product | Affected | Fixed |
|---|---|---|---|
| The Nu Html Checker | The Nu Html Checker | latest - commit:23f090a11bab8d0d4e698f1ffc197a4fe226a9cd | — |
Fixed in Linux distributions
Distributions backport fixes, so the version that fixes this vulnerability differs per release — upgrade to at least the version shown. From the distributions' security trackers and advisories.
Debian
Security tracker ↗| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| Debian 14 | vnu | No fix yet | — |
Ubuntu
Security tracker ↗| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| Ubuntu 26.10 | vnu | No fix yet | — |
Affected packages
| Ecosystem | Package | Affected | Fixed | Record |
|---|---|---|---|---|
| Maven | nu.validator:validator | <= 26.1.11 | — | GHSA-fccg-7w3p-w66f |
| npm | vnu-jar | <= 26.1.11 | — | GHSA-fccg-7w3p-w66f |
References
- https://fluidattacks.com/advisories/europe third-party-advisory
- https://github.com/validator/validator product