Collected research

HostSplit: Exploitable Antipatterns in Unicode Normalization

Jonathan Birch · i.blackhat.com

Some Unicode characters normalise under NFKC to ASCII with URL syntax meaning, so a hostname validated as a subdomain of a trusted site resolves as a different host plus a path, bypassing allow-lists and stealing OAuth tokens. HostBond is the reverse: punycode decoded for display lets an attacker domain render as a trusted host or email sender.

Record

Researcher

Jonathan Birch

Published by

i.blackhat.com

Format

Whitepaper

Topic

Other

In the archive

• Collected in the 2019 research round

Related sources

• HostSplit: Exploitable Antipatterns in Unicode Normalization

Tags

• unicode
• url-parsing
• parser-differential
• open-redirect
• oauth
• filter-bypass
• email
• encoding
• cve
• owasp-a04-2021
• owasp-a05-2021
• owasp-a07-2021

This page is the archive's own catalogue record. The research is the work of Jonathan Birch, first published at the original source. Preserved copies are kept so the citation survives its host; this one was last captured on 11 August 2026.