# Phishing URL abuses parser inconsistencies to evade filters

Published: 2026-09-24 · Severity: routine · Sectors: manufacturing
Canonical: https://vorant.io/reports/172b5987-33da-56a7-94ed-11675e10dbba/phishing-url-abuses-parser-inconsistencies-to-evade-filters

> A phishing campaign uses userinfo fields, invalid hyphenated hostnames, and embedded victim emails in one URL to evade blocklists and confuse parsers while still working in browsers.

SANS ISC handler Xavier Mertens analyzed a phishing email link that combines three obfuscation techniques in a single URL to defeat automated security tooling while remaining fully functional in browsers. The URL abuses the RFC 3986 'userinfo' field (a random string before the '@' in the authority) to make each link unique, defeating exact-match blocklists and likely serving as a per-victim tracking token. It also uses a hostname with labels starting/ending in hyphens (e.g., 'gynd--.koncar-hr.com'), which violates RFC 952/1123 hostname rules but resolves fine via DNS and browsers, causing strict validators and regex-based extractors to skip the URL entirely. The domain is a typosquat of the legitimate Croatian industrial group koncar.hr, likely using wildcard DNS to generate unique subdomains per victim.

The third trick appends the victim's own email address in the URL path, which phishing kits commonly use to pre-fill login forms and customize branding. This also causes naive parsers that split on the last '@' to misidentify the host as the victim's own trusted domain (e.g., isc.sans.edu), while WHATWG-compliant browsers correctly parse the authority up to the first '/' and connect to the attacker's actual server. The author notes attackers are not exploiting a software vulnerability but rather differences in how various tools parse URLs versus how browsers do.

For detection, the analyst recommends hunting for URLs containing more than one '@' character, hostname labels beginning or ending with hyphens, and paths containing the recipient's own email address as indicators of this technique. This is a defensive research/awareness piece with no named threat actor, malware family, or specific victim organization beyond the illustrative example.

Source reporting: https://isc.sans.edu/diary/rss/33366

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