Oracle releases security patches for Apache Struts CVE-2017

In Apache Struts 2.0.0 through 2.3.33 and 2.5 through 2.5.10.1, using an unintentional expression in a Freemarker tag instead of string literals can lead to a RCE attack.

CVE-2017-5638 is an improper input validation flaw (CWE-20) in the Jakarta Multipart parser of Apache Struts, in which the parser mishandles the Content-Type value of a file upload and allows malicious upload leading to remote code execution. It is triggered remotely without authentication by sending a crafted Content-Type header in a multipart request to a Struts endpoint; no valid upload or credentials are required. A successful attacker gains code execution in the security context of the application server, which typically enables host compromise, data theft, or ransomware deployment. Any organization running Apache Struts applications that use the Jakarta Multipart parser is affected; the provided data specifies only "Apache Struts" and gives no version ranges. Exploitation is confirmed in the wild: the flaw is listed in CISA KEV (added 2021-11-03) with known ransomware use, EPSS assigns it roughly a 100% exploitation probability (100th percentile), and no public PoC is catalogued in the source data.

Do: Apply updates per vendor instructions: upgrade Apache Struts to the releases that fix this flaw (2.3.32 / 2.5.10.1 or later, per Apache advisory S2-045), and check for Struts jars bundled inside application packages and vendor appliances. Prioritize internet-facing apps, and as an interim mitigation validate or filter the Content-Type header on multipart requests. Because exploitation is in the wild and ransomware use is known, also review web and application server logs for evidence of successful compromise.

When using a Spring AOP functionality to secure Struts actions it is possible to perform a DoS attack. Solution is to upgrade to Apache Struts version 2.5.12 or 2.3.33.

CVE-2017-9791 is an improper input validation flaw (CWE-20) in the Struts 1 plugin shipped with Apache Struts 2.1.x and 2.3.x. When a user-supplied field value is passed as a raw message to ActionMessage, it is evaluated as an expression, allowing an unauthenticated attacker to achieve remote code execution with the privileges of the Java web application. Organizations running Struts 2.1.x/2.3.x applications with the Struts 1 plugin enabled are affected, and Oracle has separately shipped patches for Struts bundled in its products. The flaw is listed in CISA's Known Exploited Vulnerabilities Catalog (added 2022-02-10) and carries a 98.9% EPSS score (100th percentile), indicating active, widespread exploitation, though no public proof-of-concept is catalogued.

Do: Apply updates per vendor instructions as required by CISA by upgrading Struts 2.1.x/2.3.x to a patched release and, where feasible, disabling or removing the Struts 1 plugin; audit application code for ActionMessage calls that pass unvalidated user input as raw messages. For Oracle products that bundle Struts, apply Oracle's Struts-related security patches. Prioritize internet-facing applications given confirmed in-the-wild exploitation (KEV) and the near-certain near-term exploitation probability (EPSS 98.9%).

CVE-2017-9805 is an unsafe deserialization vulnerability in the REST plugin of Apache Struts 2, which uses the XStream library to deserialize XML request payloads without any type filtering. An attacker triggers it by sending a crafted XML payload to an endpoint handled by the REST plugin, causing the payload to be deserialized into arbitrary objects. Successful exploitation yields remote code execution on the server with the privileges of the web application, typically enough to fully take over the host. Struts 2.1.1 through 2.3.x before 2.3.34 and 2.5.x before 2.5.13 are affected, including products from Cisco and NetApp that bundle vulnerable Struts versions. The flaw has a public proof-of-concept exploit, is on CISA's Known Exploited Vulnerabilities catalog, and was reported as under active exploitation after its 2017 disclosure, although the Apache Foundation disputed suggestions that this specific flaw was used in the Equifax breach.

Do: Upgrade Apache Struts to 2.3.34, 2.5.13, or later, or apply the fixed updates for any Cisco or NetApp product that embeds Struts per their advisories. If patching is not immediate, remove or disable the REST plugin, or restrict the XML content types it accepts. Inventory internet-facing applications for Struts REST endpoints and hunt for suspicious XML POSTs, since the CVE is on the CISA KEV list and was reported as actively exploited.