SVG Voicemail Phishing Campaign Hits 5,527
A two-month phishing campaign used SVG attachments disguised as voicemail files to deliver obfuscated JavaScript, bypassing email defenses.
A large-scale phishing campaign used scalable vector graphics (SVG) attachments disguised as voicemail notifications to deliver obfuscated JavaScript. Email security vendor INKY, part of Kaseya, detected 26,589 messages sent to 5,527 organizations between June 1 and August 4, 2026.
The campaign's largest spike occurred on June 3, when 2,432 messages reached 1,149 organizations. INKY stated the campaign was still active when its analysis concluded. The operation showed little evidence of precision targeting. The median organization received just two messages, while 32% received only one. The ten most-affected organizations accounted for only 6% of the total volume, indicating a broad spray delivery method.
SVG Smuggling Evades Detection
The lure presented itself as an internal voicemail notification. INKY's analysis found that 99.5% of email subjects incorporated the local part of the recipient's own email address. Attachments used voicemail-style names and contained SVG and XML content.
These attachments declared a MIME type of text/plain rather than the correct image/svg+xml. This meant a scanner checking only the stated type would see an innocuous text file instead of active content. This distinction was critical because SVG files can contain JavaScript. In the samples analyzed by INKY, a minimal graphic shell concealed obfuscated script that reconstructed strings at runtime and fetched a remote endpoint. The code also used deferred execution and runtime script injection, making its behavior harder to identify through static inspection.
Native Spam Filtering Largely Failed
The campaign heavily relied on internal spoofing. INKY said 95% of the messages claimed to come from the recipient's own domain while actually arriving from an external, unauthenticated sender.
Native spam scoring treated most of the campaign as harmless. A breakdown of the Microsoft Spam Confidence Level (SCL) verdicts for the messages is shown below:
| SCL Score | Number of Messages | Percentage | Microsoft Verdict |
|---|---|---|---|
| 0 or 1 | 19,994 | 75% | Not Spam |
| 5 | 4,777 | 18% | Spam |
INKY noted that the campaign was built from a single template, yet the same message drew different native verdicts depending on the receiving mailbox. These findings show how the campaign combined several individually plausible signals: a familiar voicemail pretext, an image format, recipient-specific personalization, and internal sender impersonation. The SVG attachment provided the bridge between those social-engineering elements and executable browser content.
