Description
Seeyon OA A8 contains an unauthenticated arbitrary file write vulnerability in the /seeyon/htmlofficeservlet endpoint that allows remote attackers to write arbitrary files to the web application root by sending specially crafted POST requests with custom base64-encoded payloads. Attackers can write JSP webshells to the web root and execute them through the web server to achieve arbitrary OS command execution with web server privileges. Exploitation evidence was first observed by the Shadowserver Foundation on 2021-03-26 (UTC).
References7
- sourceforge.net/software/product/A8/
- static-aliyun-doc.oss-cn-hangzhou.aliyuncs.com/download/pdf/909…
- web.archive.org/web/20190821034711/wyb0.com/posts/2019/seeyon-h…
- wiki.96.mk/Web%E5%AE%89%E5%85%A8/%E8%87%B4%E8%BF%9Coa/%E8%87%B4…
- www.broadcom.com/support/security-center/attacksignatures/detai…
- www.fortiguard.com/encyclopedia/ips/48874/seeyon-office-anywher…
- www.vulncheck.com/advisories/seeyon-office-anywhere-oa-a8-unaut…
Metrics
- CVSS 4.0
-
9.3
CRITICAL
Score source: CNA
CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X - EPSS — exploit probability
- 1% percentile: 52 · as of 13 November 2026
- CWE
- CWE-434
Could this be exploited in your environment?
A patch closes the known hole. A penetration test shows what an attacker can still reach — with proof.