ONLYOFFICE Docs: attackers can read or change files
OFFICIAL NAME: ONLYOFFICE Docs Server Path Traversal Vulnerability
WHAT IT IS · DOCUMENTS AND COLLABORATIONIt holds shared documents and internal pages.
DO THIS FIRSTPatch it, or ask your provider whether they have. Not sure if you use it? Send this page to your IT provider or security lead and ask.
TECHNICAL SUMMARY ONLYOFFICE Docs contains a path traversal vulnerability that can occur when JWT is used, via a /.. sequence in an image upload parameter and could allow for remote code execution.
WHY THIS VERDICT Attacks are confirmed. The severity score is critical (9.8).
WHY IT RANKS HERE Exploitation is confirmed by an authoritative source.
- HIGHEST CONFIRMED RUNG
- EXPLOITED
- CISA KEV
- LISTED
- EXPLOIT CODE
- NONE KNOWN
How far has it climbed?
01 TALK
▨ REPORTED, NOT CONFIRMEDNEWEST EVIDENCE · 1 SOURCECVE-2021-3199 discussed publicly (CIRCL sighting).
02 EXPOSED
□ NOT TRACKED YETNO SOURCE FOR THIS STEP YETWe have no source that counts exposed systems yet. Internet scan data needs a partnership we do not have. No evidence here does not mean nothing is exposed.
03 TRIED
■ CONFIRMEDNEWEST EVIDENCE · 2 INDEPENDENT SOURCESAttacks that worked are confirmed (step 4), so attempts count as confirmed too.
04 EXPLOITED
■ CONFIRMEDNEWEST EVIDENCE · 2 INDEPENDENT SOURCESONLYOFFICE Docs contains a path traversal vulnerability that can occur when JWT is used, via a /.. sequence in an image upload parameter and could allow for remote code execution. CISA Vulnrichment marks CVE-2021-3199 as actively exploited.
05 DAMAGE
□ NOT TRACKED YETNO SOURCE FOR THIS STEP YETBreach notices and filings rarely name the flaw that was used, so we cannot link them to this event yet. No evidence here does not mean no harm.
When each thing happened
- DISCLOSED
- EXPLOIT CODE PUBLICNOT YET
- FIRST ATTACK REPORT
- CISA KEV LISTING
- US FEDERAL DEADLINE
THE FIX
CISA's instruction: apply the vendor's fix, or stop using the product if no fix exists. The deadline CISA set for US federal agencies, Oct 11, 2026, has passed. It is a US government deadline; use it as a guide.
Questions to ask this week
- Do we run ONLYOFFICE Docs? If yes, is it patched or cut off from the internet?
- Who owns fixing it, and by what date?
- Have we checked for signs of attack since the first report, not just since the patch?
How it unfolded
- Attack activity. JAN 21, 2021CISA Vulnrichment marks CVE-2021-3199 as actively exploited
- Attack activity. OCT 7, 2026ONLYOFFICE Docs Server Path Traversal Vulnerability
- NOV 6, 2026CVE-2021-3199 discussed publicly (CIRCL sighting)
SOURCES
- [1] CIRCL Vulnerability-Lookup sightings: CVE-2021-3199 discussed publicly (CIRCL sighting), NOV 6
- [2] CISA Known Exploited Vulnerabilities: ONLYOFFICE Docs Server Path Traversal Vulnerability, OCT 7
- [3] CVE List V5 and CISA Vulnrichment: CISA Vulnrichment marks CVE-2021-3199 as actively exploited, JAN 21