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Not in CISA KEV
HIGH severity

CVE-2021-26073

HIGH

CVE-2021-26073 is a high-severity (CVSS 7.7) Improper Authentication vulnerability in atlassian connect express. O3 Security detects and blocks CVE-2021-26073 exploitation at runtime via eBPF exploit-chain detection and L7 egress monitoring, even on unpatched systems.

Broken Authentication in Atlassian Connect Express (ACE) from version 3.0.2 before version 6.6.0: Atlassian Connect Express is a Node.js package for building Atlassian Connect apps.…

Published
Apr 16, 2021
Updated
Jun 17, 2026
Affected
1 product
Patched
See advisory
Exploits
None indexed
Exploitation data as of Jun 17, 2026 · OSV.dev, NVD, FIRST.org (EPSS)

Description

Broken Authentication in Atlassian Connect Express (ACE) from version 3.0.2 before version 6.6.0: Atlassian Connect Express is a Node.js package for building Atlassian Connect apps. Authentication between Atlassian products and the Atlassian Connect Express app occurs with a server-to-server JWT or a context JWT. Atlassian Connect Express versions from 3.0.2 before 6.6.0 erroneously accept context JWTs in lifecycle endpoints (such as installation) where only server-to-server JWTs should be accepted, permitting an attacker to send authenticated re-installation events to an app.

Affected Products

1 product · 1 configurations
Application
connect expressatlassian
≥ 3.0.2 && < 6.6.0
range

Detection & mitigation playbook

Vendor / appliance
  1. Detect

    Inventory every atlassian connect express deployment and check each version against the affected-products list above. Because the exploit targets the running system rather than your application code, also watch for exploitation at the network and runtime layer — O3 flags the exploit behaviour from runtime telemetry and egress traffic even before a vulnerable build is confirmed.

  2. Fix

    Apply the atlassian connect express security patch or hotfix for CVE-2021-26073 on the affected version, following the vendor advisory for your exact build.

  3. Workarounds

    Cut exposure now: restrict the management/admin interface to trusted networks, segment the device, and apply the vendor's recommended configuration mitigations and any WAF/IPS signature. O3's runtime protection blocks the exploit chain at execution, holding the line on unpatched or end-of-life systems until you can patch.

  4. How O3 protects you

    O3 detects and blocks CVE-2021-26073 exploitation at runtime: eBPF exploit-chain detection, plus L7 egress monitoring that catches the post-exploitation callback and severs the attacker's outbound channel.

Tailored to CVE-2021-26073. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.

Frequently Asked Questions

Broken Authentication in Atlassian Connect Express (ACE) from version 3.0.2 before version 6.6.0: Atlassian Connect Express is a Node.js package for building Atlassian Connect apps. Authentication between Atlassian products and the Atlassian Connect Express app occurs with a server-to-server JWT or a context JWT. Atlassian Connect Express versions from 3.0.2 before 6.6.0 erroneously accept context JWTs in lifecycle endpoints (such as installation) where only server-to-server JWTs should be accepted, permitting an attacker to send authenticated re-installation events to an app.
O3 Security · Runtime Protection

Is CVE-2021-26073 being exploited in your environment?

O3's eBPF runtime sensors and L7 egress monitoring detect and block the CVE-2021-26073 exploit chain at execution — protecting unpatched and end-of-life systems until the vendor patch is applied.

CVE-2021-26073: Connect Express Improper… | O3 Security