critical Known exploitedREV. 01
CVE-2021-3199ONLYOFFICE Document Server — Upload Path Traversal to RCE
A directory traversal flaw in the /upload function of the OnlyOffice Document Server before 5.6.3 allows RCE through a /.. sequence in an image upload parameter, when the server uses signed web tokens (JWT). Public exploit code exists.
Read the risk
THE VITAL STATS- CVSS score
- 9.8/ 10 CVSS v3.1
- EPSS probability
- 30.2% Likelihood of exploitation
- Attack complexity
- Low Conditions needed to exploit
- Known exploited
- Yes — CISA KEV
- CVE published
- 2021-01-26
- Added to KEV
- 2026-10-08
- CISA due date
- 2026-10-11
- Exploit published
- Yes
- Confidence
- high
- Kill chain
- initial access
- MITRE ATT&CK
- T1190
- Severity
- critical
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
Attacker needsNetwork access to the /upload function of a server that uses signed web tokens.
Fixed in5.6.3
Behind the card
5 REFERENCES- 01CVE recordNVD recordnvd.nist.gov
- 02CISACISA Known Exploited Vulnerabilities catalogcisa.gov
- 03Exploitgithub.comgithub.com
- 04Exploitgithub.comgithub.com
- 05Writeupgithub.comgithub.com
Field-level provenanceTRACE THE SOURCES +
Which source supports each field, when it was retrieved, and who extracted it.
| Fields | Source | Retrieved | Extractor | Confidence |
|---|---|---|---|---|
| cvss, exploitation.attack_complexity, exploitation.exploit_available, published_at, references | nvd.nist.gov | 2026-11-05 | scrty-crds-pipeline/0.1 | high |
| exploitation.known_exploited, exploitation.kev_added, exploitation.kev_due | cisa.gov | 2026-11-05 | scrty-crds-pipeline/0.1 | high |
| epss | api.first.org | 2026-11-05 | scrty-crds-pipeline/0.1 | high |
| title, subtitle, summary, severity, remediation, mitre_attack, kill_chain, recommended_action, confidence, tags, exploitation.prerequisites | nvd.nist.gov | 2026-11-05 | claude-code | high |
Printing history
THE RECORD- r1Initial base card
History unavailable — this build has no Git history for the card file.