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    Rewterz Threat Alert – New CPDoS Web Cache Poisoning Attacks Impact Sites Using Popular CDNs

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    March 25, 2023
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    Rewterz Threat Alert – GandCrab or .CRAB Ransomware – Active IOCs
    Severity Medium Analysis Summary GandCrab – a ransomware-as-a-service variant – was discovered in early 2018. At least five versions of GandCrab have been created since its […]
    March 25, 2023
    March 25, 2023
    Rewterz Threat Alert – NJRAT – Active IOCs
    Severity Medium Analysis Summary NjRat is a Remote Access Trojan, which is found leveraging Pastebin to deliver a second-stage payload after initial infection. There are multiple […]
    March 24, 2023
    March 24, 2023
    Rewterz Threat Advisory – CVE-2023-20113 – Cisco SD-WAN vManage Software Vulnerability
    Severity Medium Analysis Summary CVE-2023-20113  Cisco SD-WAN vManage Software is vulnerable to cross-site request forgery, caused by improper validation of user-supplied input. By persuading an authenticated […]

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    Read More about XDR

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    • Rewterz XDR
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    Rewterz Threat Alert – New CPDoS Web Cache Poisoning Attacks Impact Sites Using Popular CDNs

    Managed Security Services

    • Managed Security Monitoring
    • Remote SOC
    • Onsite SOC
    • Hybrid SOC

    Managed Penetration Testing

    Rewterz penetration testing services help organizations determine if a cyber attacker can gain access to their critical assets while giving them detailed insights of the overall business impact of a cyber attack.

  • Services

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    • Compromise Assessment
    • APT Assessment
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    Transform

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    March 25, 2023
    March 25, 2023
    Rewterz Threat Alert – GandCrab or .CRAB Ransomware – Active IOCs
    Severity Medium Analysis Summary GandCrab – a ransomware-as-a-service variant – was discovered in early 2018. At least five versions of GandCrab have been created since its […]
    March 25, 2023
    March 25, 2023
    Rewterz Threat Alert – NJRAT – Active IOCs
    Severity Medium Analysis Summary NjRat is a Remote Access Trojan, which is found leveraging Pastebin to deliver a second-stage payload after initial infection. There are multiple […]
    March 24, 2023
    March 24, 2023
    Rewterz Threat Advisory – CVE-2023-20113 – Cisco SD-WAN vManage Software Vulnerability
    Severity Medium Analysis Summary CVE-2023-20113  Cisco SD-WAN vManage Software is vulnerable to cross-site request forgery, caused by improper validation of user-supplied input. By persuading an authenticated […]

    Threat Insights

    16
    pdf-file (1)
    Annual Threat Intelligence Report 2022
    • Threat Advisories
    • Monthly Threat Insights
    • Threat Intelligence Reports
  • Why Rewterz?

    About Us

    Before Rewterz got its start, the market was in dire need of a specialized and dedicated information security company. It was nearly impossible for businesses to find a trustworthy provider that could truly cover all of their bases. We wanted to meet this need, giving companies across the globe a chance to get ahead while knowing that their data is in good hands.

    Read More

    play_btn_Smallplay_btn_hover_Small
    leadership

    Our Leadership

    Our leadership team brings together years of knowledge and experience in cybersecurity to drive our company's mission and vision. Our team is passionate about delivering high-quality products and services, leading by example and assisting our clients in securing their organization’s environment.
    help

    CSR

    At Rewterz, we believe that businesses have a responsibility to impact positively and contribute to the well-being of our communities as well as the planet. That's why we are committed to operating in a socially responsible and sustainable way.

    Connect with Us

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Rewterz
Rewterz Threat Advisory – Chrome 78 Released With DoH Trial, Tab Hover Cards, and More Patches
October 23, 2019
Rewterz
Rewterz Threat Alert – Lazarus APT Group Drops Malicious PowerShell Scripts – IoCs
October 23, 2019

Rewterz Threat Alert – New CPDoS Web Cache Poisoning Attacks Impact Sites Using Popular CDNs

October 23, 2019

Severity

Medium

Analysis Summary

Web cache poisoning attacks have been discovered that could be used to deny users access to resources delivered through a content delivery network (CDN). Named Cache-Poisoned Denial of Service (CPDoS), the new method has several variations and works by sending an HTTP request with a malformed header. CDNs have the property of reducing the traffic footprint on origin servers using their services by caching resources that are requested frequently by clients. CPDoS works at the level of the intermediate cache system of a CDN, which receives and stores an error page caused by a malformed HTTP request header and works as follows.

CPDoS.png

There are three variations of the CPDoS attack:

  • HTTP Header Oversize (HHO)

With the HHO type of CPDoS attack, a threat actor takes advantage of the size limit intermediary systems and web servers set for an HTTP request header.

If the cache system accepts a request header size larger than what is defined for the origin server, the attacker can craft a request with an oversized request key or with multiple headers.

  • HTTP Meta Character (HMC)

HTTP Meta Character (HMC), the second variation of the CPDoS attack is similar to HHO but leverages a harmful meta character. These are any “control characters such as the break/carriage return (‘\n)’, line feed (‘\r’) or bell (‘\a’).” Again, the cache system does its job and forwards the request as it is received from the client. As it reaches the origin server, it may be classified as malicious and generates an error message that gets cached and presented to the client instead of the requested resource.

  • HTTP Method Override (HMO)

The method override attack (HMO), a third variation of the CPDoS, profits from intermediary systems (e.g. proxies, load balancers, caches, firewalls) supporting only the GET and POST HTTP request methods.

This translates into blocking other HTTP requests methods. A web framework that provides instructions for the web app to replace the supported HTTP method in the header allows bypassing the security policy and delivers a different one, such as DELETE.The consequence is that the error message is cached and served for subsequent valid GET requests for the /index.html resource.

The table below shows which combination of web caching systems and HTTP implementation is affected by this class of denial of service.

CPDoS_06.png

Amazon’s security team acknowledged the weaknesses in CloudFront and stopped caching error pages with the status code ‘400 Bad Request’ by default

Microsoft updated IIS Server with a fix and published details about the vulnerability (CVE-2019-0941) in June. Play Framework also patched their product against the HMO method in versions 1.5.3 and 1.4.6. Researchers have not heard back from most of the other vendors.

Impact

  • Disabling of Web Resources and Websites
  • Cache-Poisoned Denial of Service
  • Availability Compromise

Remediation

  • Follow the HTTP standard and cache only the error pages ‘404 Not Found’, ‘405 Method Not Allowed’, ‘410 Gone’ and ‘501 Not Implemented’.
  • Do not use inappropriate status codes for errors. For instance, the ‘400 Bad Request’ is used for declaring an oversized header whereas the correct one is ‘431 Request Header Fields Too Large’ and it is not cached by any system analyzed by the researchers.
  • Another mitigation against HHO and HHM CPDoS variations is to exclude error pages from being cached altogether.
  • Protective measures also include setting up a Web Application Firewall (WAF) in front of the cache to catch malicious content trying to reach the origin server.

Platform

  • Rewterz XDR
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Managed Security Services

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Assess

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  • Architecture Design & Review
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  • Social Engineering
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Transform

  • SOC Consultancy
  • SOC Maturity Assessment
  • SOC Model Evaluation
  • SOC Gap Analysis
  • SIEM Gap Analysis
  • SIEM Optimization
  • SOC Content Pack

Train

  • Simulated Cyber Attack Exercise
  • Tabletop Exercise
  • Security Awareness and Training

Respond

  • Incident Analysis
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Threat Insights

  • Threat Advisories
  • Monthly Threat Insights
  • Threat Intelligence Reports

Resources

  • Blog
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Connect With Us

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