CVE-2021-21311
CVE-2021-21311 is a security flaw in Adminer. Attackers can make Adminer send requests into the network behind it. The US Cybersecurity and Infrastructure Security Agency (CISA) added it to its catalog of flaws known to be used in attacks on 29 Sep 2025.[1]
Adminer 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. Adminer has published a fix or advice.
Description
CISA calls it a server-side request forgery in Adminer Adminer. In its words: “Adminer contains a server-side request forgery vulnerability that, when exploited, allows a remote attacker to obtain potentially sensitive information.”[1]
The CVE record adds: “Adminer is an open-source database management in a single PHP file. In adminer from version 4.0.0 and before 4.7.9 there is a server-side request forgery vulnerability. Users of Adminer versions bundling all drivers (e.g. `adminer.php`) are affected. This is fixed in version 4.7.9.”[2]
The underlying weakness is server-side request forgery (CWE-918), in MITRE’s list of common software weaknesses.
It scores 7.2 out of 10 on the Common Vulnerability Scoring System, which rates it high, scored by NVD using CVSS 3.1.[2]
Affected versions
NVD’s record doesn’t list version ranges for it; Adminer’s advisory has them[3]. CISA names the product as Adminer Adminer.
Most families won’t have Adminer; it’s for whoever looks after IT at work.
Exploitation
CISA added it to its catalog of known exploited vulnerabilities on 29 Sep 2025, 1,691 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 20 Oct 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 98%. 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
Adminer 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.Adminer 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 20 Oct 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 7.2.[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 98%.[4] |
See also
Other server-side request forgery flaws
- CVE-2026-96655, Plex Media Server: server-side request forgery (SSRF) ·
- CVE-2026-96652, Plex Media Server: server-side request forgery (SSRF) ·
- CVE-2026-83548, SonicWall SMA1000 Appliances: server-side request forgery ·
- CVE-2026-64849, MLflow: server-side request forgery ·
- CVE-2026-15409, SonicWall SMA1000 Appliances: server-side request forgery ·
Added the same day
- CVE-2025-59689, Libraesva Email Security Gateway: command injection ·
- CVE-2025-32463, Sudo: inclusion of functionality from untrusted control sphere ·
- CVE-2025-20352, Cisco IOS and IOS XE: software SNMP denial of service and remote code execution ·
- CVE-2025-10035, Fortra GoAnywhere MFT: deserialization of untrusted data ·
References
- ^ Cybersecurity and Infrastructure Security Agency. “Adminer Server-Side Request Forgery Vulnerability”. Known Exploited Vulnerabilities Catalog, added 29 Sep 2025.
- ^ National Institute of Standards and Technology. “CVE-2021-21311 Detail”. National Vulnerability Database, published 11 Feb 2021.
- ^ Adminer. Advisories and fixes: github.com.
- ^ FIRST. “Exploit Prediction Scoring System”. EPSS 0.985, percentile 99.9, 31 Oct 2026.
- CVE Program. “CVE-2021-21311”. 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.