CVE-2018-13383
MediumExploitedPublic exploitA heap buffer overflow in Fortinet FortiOS 6.0.0 through 6.0.4, 5.6.0 through 5.6.10, 5.4.0 through 5.4.12, 5.2.14 and earlier and FortiProxy 2.0.0, 1.2.8 and earlier in the SSL VPN web portal may cause the SSL VPN web service termination for logged in users due to a failure to…
Published Feb 8, 2021 · Updated Oct 21, 2025
Key Facts
Patch immediately- CVE-2018-13383 is a medium-severity vulnerability (CVSS 6.5 v3.1) affecting Fortiproxy (Fortinet), Fortios (Fortinet), Fortinet FortiOS and FortiProxy.
- It is exploited in the wild, listed in CISA KEV, Industry KEV feed, CIRCL KEV, ENISA EUVD since Oct 2, 2019 and is known to be used in ransomware campaigns. Public exploit code is available.
- EPSS estimates a 34% probability of exploitation in the next 30 days.
- Fixed versions are available, including Fortios 5.2.15, Fortiproxy 1.2.9.
- Brandefense priority: patch immediately, because it is listed as exploited in the wild.
CVSS v3.1
6.5
CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:N/A:H
EPSS (30-day exploit likelihood)
34%
Higher than 98.3% of all scored CVEs
Exploited in the wild
Yes
4 catalog listings, used by ransomware
Public exploit code
Available
Proof-of-concept or weaponized module
Get the full CVE-2018-13383 brief as a PDF
Every affected product and fixed release, exploitation status and a first 24 hours response checklist, emailed within minutes.
Description
A heap buffer overflow in Fortinet FortiOS 6.0.0 through 6.0.4, 5.6.0 through 5.6.10, 5.4.0 through 5.4.12, 5.2.14 and earlier and FortiProxy 2.0.0, 1.2.8 and earlier in the SSL VPN web portal may cause the SSL VPN web service termination for logged in users due to a failure to properly handle javascript href data when proxying webpages.
Known-Exploited Catalog Listings
| Catalog | Added | Remediation due | Ransomware use |
|---|---|---|---|
| CISA KEV | Jan 10, 2022 | Jul 10, 2022 | Known |
| Industry KEV feed | Oct 2, 2019 | Jul 10, 2022 | Known |
| CIRCL KEV | Jan 10, 2022 | Jul 10, 2022 | Known |
| ENISA EUVD | Jan 10, 2022 | n/a | Not reported |
Required action: Apply updates per vendor instructions.
Affected Products
4 affected entries in total| Product | Affected versions | Fixed in |
|---|---|---|
| FortiproxyFortinet | 2.0.0 | 1.2.9 |
| FortiosFortinet | See advisory | 5.2.15 |
| Fortinet FortiOS and FortiProxy | >= FortiOS 6.0.0 through 6.0.4, 5.6.0 through 5.6.10, 5.4.0 through 5.4.12, 5.2.14 and earlier, FortiProxy 2.0.0, 1.2.8 and earlier | n/a |
Patched Releases
Fortios
5.2.15
Fortiproxy
1.2.9
Timeline
Added to Industry KEV feed
Oct 2, 2019
Publicly disclosed
Feb 8, 2021
Added to CISA KEV
Jan 10, 2022
Added to CIRCL KEV
Jan 10, 2022
Added to ENISA EUVD
Jan 10, 2022
Last updated
Oct 21, 2025
Weakness Type
- CWE-787 Out-of-bounds Write
References
- advisoryhttps://fortiguard.com/advisory/FG-IR-18-388
- advisoryhttps://fortiguard.com/advisory/FG-IR-20-229
- advisoryhttps://www.bleepingcomputer.com/news/security/fortinet-fixes-critical-vulnerabilities-in-ssl-vpn-and-web-firewall/
- advisoryUSOM advisory
- exploitVulnCheck exploitation report
FAQ
Common Questions.
A heap buffer overflow in Fortinet FortiOS 6.0.0 through 6.0.4, 5.6.0 through 5.6.10, 5.4.0 through 5.4.12, 5.2.14 and earlier and FortiProxy 2.0.0, 1.2.8 and earlier in the SSL VPN web portal may cause the SSL VPN web service termination for logged in users due to a failure to properly handle javascript href data whe…
Affected: Fortiproxy (Fortinet) versions 2.0.0; Fortios (Fortinet); Fortinet FortiOS and FortiProxy versions >= FortiOS 6.0.0 through 6.0.4, 5.6.0 through 5.6.10, 5.4.0 through 5.4.12, 5.2.14 and earlier, FortiProxy 2.0.0, 1.2.8 and earlier. The full list is in the CVE brief.
It is exploited in the wild, listed in CISA KEV, Industry KEV feed, CIRCL KEV, ENISA EUVD since Oct 2, 2019 and is known to be used in ransomware campaigns.
Yes. It was added on Jan 10, 2022 with a federal remediation due date of Jul 10, 2022.
Public exploit code is available.
Fixed versions are available, including Fortios 5.2.15, Fortiproxy 1.2.9.
Brandefense priority: patch immediately, because it is listed as exploited in the wild.
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