CVE-2023-27294Public exploitNetwork attack vector

Session theft via unsanitized calendar event descriptions

Published Feb 28, 2023 · Updated Mar 21, 2025

Stored XSS in the OpenCATS 0.9.6 calendar allows remote authenticated users to steal session tokens via crafted event descriptions. The addEvent flow stores the description parameter without sufficient sanitization and renders it as active JavaScript when another user views the event. A restricted account is sufficient, but exploitation requires another user to browse to the poisoned event; stolen higher-privilege sessions or actions in the victim's session are bounded impacts.

CVSS severity5.4
Medium
EPSS probability0.53%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Stored XSS in the OpenCATS 0.9.6 calendar allows remote authenticated users to steal session tokens via crafted event descriptions. The addEvent flow stores the description parameter without sufficient sanitization and renders it as active JavaScript when another user views the event. A restricted account is sufficient, but exploitation requires another user to browse to the poisoned event; stolen higher-privilege sessions or actions in the victim's session are bounded impacts.

The record

CVE
CVE-2023-27294
Published
Feb 28, 2023
Updated
Mar 21, 2025
Vendor
OpenCATS
Product
OpenCATS
Classifications
CWE-79, T1539
Attack vector
network
Privileges
authenticated

Timeline

How it unfolded

  1. Feb 28, 2023CVE publishedPublication date reported by the CVE source.
  2. Mar 21, 2025Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=0.9.6

What conditions does exploitation require?

Attack vectornetwork
Required privilegesauthenticated

What is affected?

OpenCATS · OpenCATSversion=0.9.6

Published CVSS scores

5.4NIST NVDCVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:C/C:L/I:L/A:N
5.4CISA-ADPCVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:C/C:L/I:L/A:N

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesauthenticated
Known exploitationUnconfirmed
Public exploitPublished

Weakness, pattern, technique

CWE-79Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')
T1539Steal Web Session Cookie

Public exploit references

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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