CVE-2025-59718
CVE-2025-59718 is a security flaw in Fortinet products, Fortinet’s business security equipment. Attackers are using a flaw in Fortinet products. The US Cybersecurity and Infrastructure Security Agency (CISA) added it to its catalog of flaws known to be used in attacks on 16 Dec 2025.[1]
Fortinet products is business software or equipment. Most families won’t have it, but attackers break into it to get inside companies, and from there to what those companies hold about their customers, patients and staff. Fortinet has published a fix or advice.
Description
CISA calls it an improper verification of cryptographic signature in Fortinet Multiple Products. In its words: “Fortinet FortiOS, FortiSwitchMaster, FortiProxy, and FortiWeb contain an improper verification of cryptographic signature vulnerability that may allow an unauthenticated attacker to bypass the FortiCloud SSO login authentication via a crafted SAML message. Please be aware that CVE-2025-59719 pertains to the same problem and is mentioned in the same vendor advisory. Ensure to apply all patches mentioned in the advisory.”[1]
The CVE record adds: “A improper verification of cryptographic signature vulnerability in Fortinet FortiOS 7.6.0 through 7.6.3, FortiOS 7.4.0 through 7.4.8, FortiOS 7.2.0 through 7.2.11, FortiOS 7.0.0 through 7.0.17, FortiProxy 7.6.0 through 7.6.3, FortiProxy 7.4.0 through 7.4.10, FortiProxy 7.2.0 through 7.2.14, FortiProxy 7.0.0 through 7.0.21, FortiSwitchManager 7.2.0 through 7.2.6, FortiSwitchManager 7.0.0 through 7.0.5 allows an unauthenticated attacker to bypass the FortiCloud SSO login authentication via a crafted SAML response message.”[2]
The underlying weakness is CWE-347, in MITRE’s list of common software weaknesses.
It scores 9.8 out of 10 on the Common Vulnerability Scoring System, which rates it critical, scored by the organisation that published the CVE using CVSS 3.1.[2]
Affected versions
NVD’s record doesn’t list version ranges for it; Fortinet’s advisory has them[3]. CISA names the product as Fortinet Multiple Products.
Most families won’t have Fortinet products; it’s for whoever looks after IT at work.
Exploitation
CISA added it to its catalog of known exploited vulnerabilities on 16 Dec 2025, 7 days after it was made public. CISA lists a flaw only when it has reliable evidence of it being exploited, and gave US federal agencies until 23 Dec 2025 to fix it.[1]
FIRST’s Exploit Prediction Scoring System, which estimates how likely a flaw is to be used in attacks in the next 30 days from what it sees across the internet, puts it at 68%. That’s in the top 1% of the flaws it scores.[4]
CISA assesses it as automatable: attackers can run it against many targets at once.
CISA doesn’t say who was attacked, or how.
Fix
Fortinet has published a fix or advice.[3] CISA’s required action: “Apply mitigations per vendor instructions, follow applicable BOD 22-01 guidance for cloud services, or discontinue use of the product if mitigations are unavailable.”[1]
- Check whether you use it.Fortinet products is business software or equipment, so most families won’t have it. If you run a business, or work from home on company equipment, ask whoever looks after your IT.
- Send this page to your IT person.Ask them to confirm it’s fixed, or not in use. CISA gave US government agencies until 23 Dec 2025 to fix it.
- If it can’t be fixed, take it offline.CISA’s advice when there’s no fix is to stop using the product, or take it off the internet, until there is one.
You can’t fix someone else’s server, but you can watch for what follows a break-in like this: a breach notice, a password reset you didn’t ask for, or a scam message that knows things it shouldn’t. HARD watches for those for you and your family.
Timeline
| Date | Event |
|---|---|
| The flaw is made public in the National Vulnerability Database, with a severity score of 9.8.[2] | |
| CISA adds it to its catalog of flaws known to be used in attacks.[1] | |
| CISA’s deadline for US government agencies to fix it.[1] | |
| FIRST puts the odds of it being used in attacks in the next 30 days at 68%.[4] |
See also
Other Fortinet products flaws
- CVE-2025-61624: path traversal ·
- CVE-2025-25249: heap-based buffer overflow ·
- CVE-2026-24858: authentication bypass using an alternate path or channel ·
- CVE-2025-32756: stack-based buffer overflow ·
- CVE-2024-23113: format string ·
- CVE-2022-40684: authentication bypass ·
Other Fortinet flaws
- CVE-2026-104286, Fortinet FortiMail: path traversal ·
- CVE-2025-68686, Fortinet FortiOS: exposure of sensitive information to an unauthorized actor ·
- CVE-2026-39808, Fortinet FortiSandbox: OS command injection ·
- CVE-2026-25089, Fortinet FortiSandbox: OS command injection ·
- CVE-2026-21643, Fortinet FortiClient EMS: SQL injection ·
Similar flaws
- CVE-2026-5430, WSO2 products: path traversal ·
- CVE-2026-48558, SimpleHelp: authentication bypass ·
- CVE-2020-2021, Palo Alto Networks PAN-OS: authentication bypass ·
- CVE-2022-20703, Cisco Small Business RV160, RV260, RV340, and RV345 Series Routers: small business RV series routers stack-based buffer overflow ·
- CVE-2020-1464, Microsoft Windows: spoofing ·
Every Fortinet flaw on CISA’s list · Everything added in December 2025
References
- ^ Cybersecurity and Infrastructure Security Agency. “Fortinet Multiple Products Improper Verification of Cryptographic Signature Vulnerability”. Known Exploited Vulnerabilities Catalog, added 16 Dec 2025.
- ^ National Institute of Standards and Technology. “CVE-2025-59718 Detail”. National Vulnerability Database, published 9 Dec 2025.
- ^ Fortinet. Advisories and fixes: fortiguard.fortinet.com, docs.fortinet.com.
- ^ FIRST. “Exploit Prediction Scoring System”. EPSS 0.683, percentile 99.3, 31 Oct 2026.
- CVE Program. “CVE-2025-59718”. The official CVE record.
This article is built from CISA’s catalog (version 2026.10.30), NVD’s record and FIRST’s scores, kept in HARD’s database and checked every morning. The plain English is HARD’s.