CVE-2018-13383: Fortinet FortiOS and FortiProxy Out-of-bounds Write
- Is it exploited?
Yes. CISA added it to the Known Exploited Vulnerabilities catalog on 10 Jan 2022, 957 days after the CVE record was published.
- How likely is exploitation in the next 30 days?
- 32.5%
EPSS score, percentile 98.3 of all scored records
- How severe?
- 4.3 Medium
CVSS v3.1 base score, given by the CNA
- What should I do?
CISA deadline 10 Jul 2022. Apply updates per vendor instructions.
The CVE record links no vendor advisory, patch or mitigation.
- Which versions are affected?
Affected
- 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…
Source: CISA Known Exploited Vulnerabilities (KEV) catalog, 2026.10.28, as of 28 Oct 2026; FIRST Exploit Prediction Scoring System (EPSS), v2026.06.15, as of 28 Oct 2026; CVE List V5 (CVE Program), cve_2026-10-28_0000Z, as of 28 Oct 2026. About the data.
What to do
Required action, set by CISA
Apply updates per vendor instructions.
CISA due date for this action: 10 July 2022.
Advisories and patches
The CVE record links no vendor advisory, patch or mitigation.
Linked from CISA's catalog entry
Affected products and versions
As listed in the CVE record.
| Status | Versions |
|---|---|
| Affected | 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… |
Source: CVE List V5 (CVE Program), cve_2026-10-28_0000Z, as of 28 Oct 2026. About the data.
About this vulnerability
A heap buffer overflow in Fortinet FortiOS and FortiProxy may cause the SSL VPN web service termination for logged in users.
Summary: CISA's KEV catalog, as of 28 Oct 2026.
- CISA added CVE-2018-13383 to its Known Exploited Vulnerabilities (KEV) catalog on 10 Jan 2022.
- CISA marks it as known to be used in ransomware campaigns.
- The due date CISA sets for the required action is 10 Jul 2022.
- The CVE record was published on 29 May 2019, 957 days before it was added to KEV.
- The CVE record carries a CVSS v3.1 base score of 4.3 (Medium), given by its CNA.
- FIRST's EPSS model puts the probability of exploitation in the next 30 days at 32.5% (percentile 98.3), as of 28 Oct 2026.
- CISA's SSVC assessment in the CVE record: exploitation active, automatable no, technical impact partial.
Source: CISA Known Exploited Vulnerabilities (KEV) catalog, 2026.10.28, as of 28 Oct 2026; CVE List V5 (CVE Program), cve_2026-10-28_0000Z, as of 28 Oct 2026; FIRST Exploit Prediction Scoring System (EPSS), v2026.06.15, as of 28 Oct 2026. About the data.
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.
Source: CVE List V5 (CVE Program), cve_2026-10-28_0000Z, as of 28 Oct 2026. About the data.
Weakness
- CWE-787: Out-of-bounds Write
CWE and CAPEC are maintained by MITRE; the entries are those named in the CVE record and the KEV entry.
Timeline
| Date | Event |
|---|---|
| 29 May 2019 | CVE record published |
| 10 Jan 2022 | Added to CISA KEV |
| 10 Jul 2022 | CISA due date for the required action |
| 21 Oct 2025 | CVE record last updated |
References
More exploited Fortinet vulnerabilities
- CVE-2025-61624: Fortinet Multiple Products Path Traversal Vulnerability
- CVE-2026-104286: Fortinet FortiMail Path Traversal Vulnerability
- CVE-2025-25249: Fortinet Multiple Products Heap-based Buffer Overflow Vulnerability
- CVE-2025-68686: Fortinet FortiOS Exposure of Sensitive Information to an Unauthorized Actor Vulnerability
- CVE-2026-25089: Fortinet FortiSandbox OS Command Injection Vulnerability
- CVE-2026-39808: Fortinet FortiSandbox OS Command Injection Vulnerability