Fortinet FortiMail: attackers can read or change files
OFFICIAL NAME: Fortinet FortiMail Path Traversal Vulnerability
WHAT IT IS · VPN, FIREWALL OR GATEWAYIt sits at the edge of your network and faces the internet, so attackers can reach it directly.
DO THIS FIRSTIf you have it, patch it today. If you cannot, block access to it from the internet until you can. Not sure if you use it? Send this page to your IT provider or security lead and ask.
TECHNICAL SUMMARY Fortinet FortiMail contains a path traversal and an improper neutralization of NULL byte or NULL character vulnerability that may allow an unauthenticated attacker to write arbitrary files on the underlying system via crafted HTTP or HTTPS requests.
WHY THIS VERDICT Attacks are confirmed. The vulnerability is 40 days old, so many systems are likely still unpatched. The severity score is critical (9.8).
WHY IT RANKS HERE Exploitation is confirmed by an authoritative source. The product faces the internet or gives remote access.
- HIGHEST CONFIRMED RUNG
- EXPLOITED
- CISA KEV
- LISTED
- EXPLOIT CODE
- PROOF OF CONCEPT
How far has it climbed?
01 TALK
▨ REPORTED, NOT CONFIRMEDNEWEST EVIDENCE · 1 SOURCECVE-2026-104286 discussed publicly (CIRCL sighting). CVE-2026-104286 discussed publicly (CIRCL sighting).
02 EXPOSED
□ NOT TRACKED YETNO SOURCE FOR THIS STEP YETWe have no source that counts exposed systems yet. Internet scan data needs a partnership we do not have. No evidence here does not mean nothing is exposed.
03 TRIED
■ CONFIRMEDNEWEST EVIDENCE · 2 INDEPENDENT SOURCESAttacks that worked are confirmed (step 4), so attempts count as confirmed too.
04 EXPLOITED
■ CONFIRMEDNEWEST EVIDENCE · 2 INDEPENDENT SOURCESCISA Vulnrichment marks CVE-2026-104286 as actively exploited. Fortinet FortiMail contains a path traversal and an improper neutralization of NULL byte or NULL character vulnerability that may allow an unauthenticated attacker to write arbitrary files on the underlying system via crafted HTTP or HTTPS requests.
05 DAMAGE
□ NOT TRACKED YETNO SOURCE FOR THIS STEP YETBreach notices and filings rarely name the flaw that was used, so we cannot link them to this event yet. No evidence here does not mean no harm.
When each thing happened
- DISCLOSED
- EXPLOIT CODE PUBLIC
- FIRST ATTACK REPORT
- CISA KEV LISTING
- US FEDERAL DEADLINE
THE FIX
CISA's instruction: apply the vendor's fix, or stop using the product if no fix exists. The deadline CISA set for US federal agencies, Oct 4, 2026, has passed. It is a US government deadline; use it as a guide.
Questions to ask this week
- Do we run Fortinet FortiMail? If yes, is it patched or cut off from the internet?
- Who owns fixing it, and by what date?
- Have we checked for signs of attack since the first report, not just since the patch?
How it unfolded
- Attack activity. SEP 30, 2026Fortinet FortiMail Path Traversal Vulnerability
- Attack activity. OCT 1, 2026CISA Vulnrichment marks CVE-2026-104286 as actively exploited
- OCT 1, 20264 public GitHub repositories claim a proof of concept for CVE-2026-104286
- OCT 24, 2026Public proof of concept for CVE-2026-104286 (CIRCL sighting) (2 reports, latest OCT 29)
- OCT 24, 2026CVE-2026-104286 discussed publicly (CIRCL sighting) (8 reports, latest NOV 4)
SOURCES
- [1] CIRCL Vulnerability-Lookup sightings: CVE-2026-104286 discussed publicly (CIRCL sighting), NOV 4
- [2] CIRCL Vulnerability-Lookup sightings: Public proof of concept for CVE-2026-104286 (CIRCL sighting), OCT 29
- [3] PoC-in-GitHub: 4 public GitHub repositories claim a proof of concept for CVE-2026-104286, OCT 1
- [4] CVE List V5 and CISA Vulnrichment: CISA Vulnrichment marks CVE-2026-104286 as actively exploited, OCT 1
- [5] CISA Known Exploited Vulnerabilities: Fortinet FortiMail Path Traversal Vulnerability, SEP 30
- [6] CIRCL Vulnerability-Lookup sightings: 8 more reports