CVE-2015-3306
CVE-2015-3306 is a security flaw in ProFTPD. Attackers can reach parts of ProFTPD that should be locked to them. The US Cybersecurity and Infrastructure Security Agency (CISA) added it to its catalog of flaws known to be used in attacks on 8 Oct 2026.[1]
ProFTPD 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. ProFTPD has published a fix or advice.
Description
CISA calls it an improper access control in ProFTPD ProFTPD. In its words: “ProFTPD contains an improper access control vulnerability that could allow remote attackers to read and write to arbitrary files via the site cpfr and site cpto commands.”[1]
The underlying weakness is improper access control (CWE-284), in MITRE’s list of common software weaknesses.[2]
It scores 10.0 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; ProFTPD’s advisory has them[3]. CISA names the product as ProFTPD ProFTPD.
Most families won’t have ProFTPD; it’s for whoever looks after IT at work.
Exploitation
CISA added it to its catalog of known exploited vulnerabilities on 8 Oct 2026, 4,161 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 11 Oct 2026 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 99%. 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
ProFTPD has published a fix or advice.[3] CISA’s required action: “Apply mitigations in accordance with vendor instructions, ensuring compliance with CISA’s BOD 26-04 Prioritizing Security Updates Based on Risk (see URL in Notes) guidance and CISA’s “Forensics Triage Requirements” (see URL in Notes).”[1]
- Check whether you use it.ProFTPD 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 11 Oct 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 10.0.[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 99%.[4] |
See also
Other improper access control flaws
- CVE-2026-21962, Oracle HTTP Server and Oracle Weblogic Server Proxy Plug-in: improper access control ·
- CVE-2026-56290, Joomlack Page Builder: improper access control ·
- CVE-2026-34908, Ubiquiti UniFi OS: improper access control ·
- CVE-2026-48907, Widget Factory Joomla Content Editor: improper access control ·
- CVE-2026-35616, Fortinet FortiClient EMS: improper access control ·
Added the same day
- CVE-2023-22894, Strapi: cleartext storage of sensitive information ·
- CVE-2021-3199, ONLYOFFICE Docs: server path traversal ·
- CVE-2016-3081, Apache Struts: command injection ·
- CVE-2015-5477, ISC BIND: data processing errors ·
References
- ^ Cybersecurity and Infrastructure Security Agency. “ProFTPD Improper Access Control Vulnerability”. Known Exploited Vulnerabilities Catalog, added 8 Oct 2026.
- ^ National Institute of Standards and Technology. “CVE-2015-3306 Detail”. National Vulnerability Database, published 18 May 2015.
- ^ ProFTPD. Advisories and fixes: lists.debian.org, lists.opensuse.org.
- ^ FIRST. “Exploit Prediction Scoring System”. EPSS 0.995, percentile 99.9, 31 Oct 2026.
- CVE Program. “CVE-2015-3306”. 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.