CVE-2025-71389Known exploitationPublic exploitNetwork attack vector

Unauthenticated code execution via prototype traversal

Published Jul 23, 2026 · Updated Jul 23, 2026

Code injection in Cal.com Cal.diy before 5.9.9 allows remote attackers to execute arbitrary code through crafted RSC requests. The bundled Next.js React Flight decoder follows attacker-supplied object paths without an own-property check, allowing prototype-chain access to the Function constructor during deserialization. Network access to a self-hosted instance is sufficient; neither authentication nor user interaction is required, and code runs in the server process.

CVSS severity10.0
Critical
EPSS probability1.20%
Next 30 days · Sep 16, 2026
Known exploitationReported
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Code injection in Cal.com Cal.diy before 5.9.9 allows remote attackers to execute arbitrary code through crafted RSC requests. The bundled Next.js React Flight decoder follows attacker-supplied object paths without an own-property check, allowing prototype-chain access to the Function constructor during deserialization. Network access to a self-hosted instance is sufficient; neither authentication nor user interaction is required, and code runs in the server process.

The record

CVE
CVE-2025-71389
Published
Jul 23, 2026
Updated
Jul 23, 2026
Vendor
Cal.com, Inc.
Product
Cal.diy
Classifications
CWE-94, T1190
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Dec 10, 2025Exploitation reportedReported compromise of a self-hosted Cal.com instance
  2. Jul 23, 2026CVE publishedPublication date reported by the CVE source.
  3. Jul 23, 2026Record 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 <5.9.9

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Cal.com, Inc. · Cal.diyversion=0 <5.9.9

Published CVSS scores

10.0National Vulnerability DatabaseCVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:H/VA:H/SC:H/SI:H/SA:H
10.0Cal.comCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:H

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
Privilegesunauthenticated
Known exploitationReported
Public exploitPublished

Weakness, pattern, technique

CWE-94Improper Control of Generation of Code ('Code Injection')
T1190Exploit Public-Facing Application

Public exploit references

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

Reported exploitation

Technologies

Your stack

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Your stack

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