close
close
Your Network of Tomorrow
Your Network of Tomorrow
Plan your path toward a faster, more secure, and more resilient network designed for the applications and users that you support.
          Experience Netskope
          Get Hands-on With the Netskope Platform
          Here's your chance to experience the Netskope One single-cloud platform first-hand. Sign up for self-paced, hands-on labs, join us for monthly live product demos, take a free test drive of Netskope Private Access, or join us for a live, instructor-led workshops.
            A Leader in SSE. Now a Leader in Single-Vendor SASE.
            A Leader in SSE. Now a Leader in Single-Vendor SASE.
            Netskope debuts as a Leader in the Gartner® Magic Quadrant™ for Single-Vendor SASE
              Securing Generative AI for Dummies
              Securing Generative AI for Dummies
              Learn how your organization can balance the innovative potential of generative AI with robust data security practices.
                Modern data loss prevention (DLP) for Dummies eBook
                Modern Data Loss Prevention (DLP) for Dummies
                Get tips and tricks for transitioning to a cloud-delivered DLP.
                  Modern SD-WAN for SASE Dummies Book
                  Modern SD-WAN for SASE Dummies
                  Stop playing catch up with your networking architecture
                    Understanding where the risk lies
                    Advanced Analytics transforms the way security operations teams apply data-driven insights to implement better policies. With Advanced Analytics, you can identify trends, zero in on areas of concern and use the data to take action.
                        The 6 Most Compelling Use Cases for Complete Legacy VPN Replacement
                        The 6 Most Compelling Use Cases for Complete Legacy VPN Replacement
                        Netskope One Private Access is the only solution that allows you to retire your VPN for good.
                          Colgate-Palmolive Safeguards its "Intellectual Property” with Smart and Adaptable Data Protection
                          Colgate-Palmolive Safeguards its "Intellectual Property” with Smart and Adaptable Data Protection
                            Netskope GovCloud
                            Netskope achieves FedRAMP High Authorization
                            Choose Netskope GovCloud to accelerate your agency’s transformation.
                              Let's Do Great Things Together
                              Netskope’s partner-centric go-to-market strategy enables our partners to maximize their growth and profitability while transforming enterprise security.
                                Netskope solutions
                                Netskope Cloud Exchange
                                Netskope Cloud Exchange (CE) provides customers with powerful integration tools to leverage investments across their security posture.
                                  Netskope Technical Support
                                  Netskope Technical Support
                                  Our qualified support engineers are located worldwide and have diverse backgrounds in cloud security, networking, virtualization, content delivery, and software development, ensuring timely and quality technical assistance
                                    Netskope video
                                    Netskope Training
                                    Netskope training will help you become a cloud security expert. We are here to help you secure your digital transformation journey and make the most of your cloud, web, and private applications.

                                      CVE-2021-45105: New DoS Vulnerability Found in Apache Log4j

                                      Dec 20 2021

                                      Summary

                                      Just a few days after CVE-2021-45046 was released and fixed, a third zero-day vulnerability was discovered in Apache Log4j, tracked as CVE-2021-45105. The bug was reported on December 15, 2021, and disclosed on December 18, 2021. 

                                      This third vulnerability has received a CVSS score of 7.5 out of 10, whereas the first one known as Log4Shell (CVE-2021-44228) received the maximum CVSS score of 10 due to its criticality. The second vulnerability (CVE-2021-45046) had received a CVSS score of 3.7 initially but was later changed to 9.0, as it could also allow Remote Code Execution attacks.

                                      This security issue affects Apache Log4j versions ​​2.0-beta9 to 2.16.0 and could allow attackers with ​​control over the Thread Context Map (MDC) input data to perform a DoS attack. Although this bug lies in the same library, it’s not a variant from Log4Shell, as it can also abuse non-JNDI lookups. 

                                      CVE-2021-45105

                                      An attacker with input control (e.g. through the Thread Context Map) can create a malicious lookup variable that will cause an infinite recursive lookup, resulting in a process crash and DoS (Denial of Service).

                                      Screenshot of method abused by CVE-2021-45105.
                                      Method abused by CVE-2021-45105.

                                      This is possible because when a nested variable is replaced by the “StrSubstitutor” class, the “substitute()” method is called recursively. Therefore, if the nested variable references the variable itself, the substitution flow causes an infinite recursion that results in a process crash.

                                      For example, given the following Pattern Layout with the Context Lookup of  “${ctx.loginId}”, if we assign the value as “${${ctx:loginId}}”, the code will be recursively substituted in an infinite loop.

                                      Screenshot of an example of a crash caused by CVE-2021-45105.
                                      Example of a crash caused by CVE-2021-45105.

                                      A complete analysis of the vulnerability was released by the Zero Day Initiative.

                                      Conclusion

                                      Organizations have likely already upgraded Log4j twice in the past 10 days and should upgrade Log4j again to address this new vulnerability. Attackers have been exploiting the first two Log4j vulnerabilities since they were disclosed and will soon start exploiting this latest vulnerability.

                                      Protection

                                      Netskope Threat Labs is actively monitoring this campaign and will ensure coverage for all known threat indicators and payloads. 

                                      Update/Patch

                                      CVE-2021-45105 was fixed in Log4j 2.17.0, we strongly recommend everyone to update Apache Log4j to this latest version. This issue can also be mitigated by changing your logging configuration to either replace Context Lookups like ${ctx:loginId} or $${ctx:loginId} with Thread Context Map patterns (%X, %mdc, or %MDC), or by removing references to Context Lookups like ${ctx:loginId} or $${ctx:loginId} where they are sourced from external inputs, such as HTTP headers or other user inputs.

                                      Netskope Private Access

                                      If you are running internal applications that cannot be immediately patched, you can mitigate the risk of exploitation by limiting access to the app. A private access solution, such as Netskope Private Access, can be used to make private apps invisible to external attackers who seek to exploit vulnerable services. Furthermore, a private access solution can restrict access to a private app internally, such that only authorized users are able to access the app, reducing the risk that a compromised user or device could be used to exploit vulnerable services.

                                      author image
                                      Gustavo Palazolo
                                      Gustavo Palazolo is an expert in malware analysis, reverse engineering and security research, working many years in projects related to electronic fraud protection.
                                      Gustavo Palazolo is an expert in malware analysis, reverse engineering and security research, working many years in projects related to electronic fraud protection.

                                      Stay informed!

                                      Subscribe for the latest from the Netskope Blog