CVE-2025-26399
CVE-2025-26399 is a security flaw in SolarWinds Web Help Desk, SolarWinds’ IT management software. Attackers can run their own code on SolarWinds Web Help Desk from anywhere, without logging in. The US Cybersecurity and Infrastructure Security Agency (CISA) added it to its catalog of flaws known to be used in attacks on 9 Mar 2026, and says ransomware gangs have used it.[1]
SolarWinds Web Help Desk 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. SolarWinds has published a fix or advice.
Description
CISA calls it a deserialization of untrusted data in SolarWinds Web Help Desk. In its words: “SolarWinds Web Help Desk contain a deserialization of untrusted data vulnerability in AjaxProxy that could allow an attacker to run commands on the host machine.”[1]
The CVE record adds: “SolarWinds Web Help Desk was found to be susceptible to an unauthenticated AjaxProxy deserialization remote code execution vulnerability that, if exploited, would allow an attacker to run commands on the host machine. This vulnerability is a patch bypass of CVE-2024-28988, which in turn is a patch bypass of CVE-2024-28986.”[2]
The underlying weakness is deserialization of untrusted data (CWE-502), 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 NVD using CVSS 3.1.[2]
Affected versions
NVD’s record doesn’t list version ranges for it; SolarWinds’s advisory has them[3]. CISA names the product as SolarWinds Web Help Desk.
Most families won’t have SolarWinds Web Help Desk; it’s for whoever looks after IT at work.
Exploitation
CISA added it to its catalog of known exploited vulnerabilities on 9 Mar 2026, 167 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 12 Mar 2026 to fix it.[1] CISA says ransomware gangs have used it.
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 90%. 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
SolarWinds 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.SolarWinds Web Help Desk 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 12 Mar 2026 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, noting that ransomware gangs have used it.[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 90%.[4] |
See also
Other SolarWinds Web Help Desk flaws
- CVE-2025-40536: security control bypass ·
- CVE-2025-40551: deserialization of untrusted data ·
- CVE-2024-28987: hardcoded credential ·
- CVE-2024-28986: deserialization of untrusted data ·
Other SolarWinds flaws
- CVE-2026-28318, SolarWinds Serv-U: uncontrolled resource consumption ·
- CVE-2024-28995, SolarWinds Serv-U: path traversal ·
- CVE-2021-35247, SolarWinds Serv-U: improper input validation ·
- CVE-2021-35211, SolarWinds Serv-U: remote code execution ·
- CVE-2020-10148, SolarWinds Orion: authentication bypass ·
Other deserialization of untrusted data flaws
- CVE-2021-23758, Ajax.NET Professional: deserialization of untrusted data ·
- CVE-2026-63077, JetBrains TeamCity: deserialization of untrusted data ·
- CVE-2026-50522, Microsoft SharePoint: deserialization of untrusted data ·
- CVE-2026-58644, Microsoft SharePoint: deserialization of untrusted data ·
- CVE-2026-45659, Microsoft SharePoint Server: deserialization of untrusted data ·
Added the same day
- CVE-2026-1603, Ivanti Endpoint Manager (EPM): authentication bypass ·
- CVE-2021-22054, Omnissa Workspace One UEM: workspace ONE server-side request forgery ·
Every SolarWinds flaw on CISA’s list · Everything added in March 2026
References
- ^ Cybersecurity and Infrastructure Security Agency. “SolarWinds Web Help Desk Deserialization of Untrusted Data Vulnerability”. Known Exploited Vulnerabilities Catalog, added 9 Mar 2026.
- ^ National Institute of Standards and Technology. “CVE-2025-26399 Detail”. National Vulnerability Database, published 23 Sep 2025.
- ^ SolarWinds. Advisories and fixes: solarwinds.com, documentation.solarwinds.com, solarwinds.com.
- ^ FIRST. “Exploit Prediction Scoring System”. EPSS 0.901, percentile 99.8, 31 Oct 2026.
- CVE Program. “CVE-2025-26399”. 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.