Posted by Daniel Owens via Fulldisclosure on Nov 04The Apache Struts2 Tiles plugin version <=7.4.0 (and >=6.3.0) codebase includes a `ViewPreparer` construct, replete with multiple ViewPreparer factories, that contains several important vulnerabilities including unsynchronised, unbounded caches. The lack of proper synchronisation means that certain factories will create caches that race, risking lost cache entries, corrupted internal bucket states under load (this can result in infinite...

Posted by Daniel Owens via Fulldisclosure on Nov 01Description Apache Struts2 Core version 7.4.0 and below fails to properly prevent integer overflows, causing wrap-arounds and other issues on a downstream forced casting into types smaller than `BigInteger`. Importantly, this finding underscores why all applications using Struts and other such platforms should perform their own input validation checks and not blindly assume that the upstream Struts2 code has done as such, but the finding also...

Posted by Daniel Owens via Fulldisclosure on Nov 01Description The Apache Struts2 Core 7.4.0 and below performs session token comparisons cryptographically insecure early-exit comparison functions (e.g., `!=`, `memcmp`, byte-by-byte loops with `break`) that return as soon as the first mismatched byte is encountered. The execution time of the comparison is therefore proportional to the number of leading bytes that match, creating a measurable timing side-channel. Importantly, this...

Posted by Daniel Owens via Fulldisclosure on Nov 01Description Apache Struts2 Core version 7.4.0 and below's `FetchMetadataInterceptor`, `CoepInterceptor`, and `CoopInterceptor` each compare their `exemptedPaths` configuration -- a per-interceptor-reference, administrator-supplied set of paths intended to exempt specific actions from the corresponding cross-origin protection -- against `HttpServletRequest.getContextPath()`. `getContextPath()` is fixed for the entire deployed web...

Posted by Daniel Owens via Fulldisclosure on Nov 01Description The Apache Struts2 REST Plugin's (version 7.4.0 and below) `ContentTypeInterceptor.intercept(ActionInvocation)` only deserialises a request body and enforces the `struts.rest.content.maxLength` bound when `HttpServletRequest#getContentLength()` returns a positive value. `getContentLength()` returns `-1` whenever the `Content-Length` header is absent, which normal and appropriate for any Hypertext Transfer Protocol (HTTP)...

Posted by Daniel Owens via Fulldisclosure on Nov 01Description The Apache Struts2 REST Plugin's `DefaultContentTypeHandlerManager.getHandlerForResponse(HttpServletRequest, HttpServletResponse)` splits the `Accept` header on commas and passes each resulting token directly to `findHandler(String)` without trimming leading or trailing whitespace. `findHandler(String)` only retries a trimmed lookup when a token contains a semicolon (`;`), so a token that merely carries a leading space has no...

Posted by Daniel Owens via Fulldisclosure on Nov 01Description Apache Struts2 Core version 7.4.0 and below attempt to prevent arbitrary code execution via Object-Graph Navigation Language (OGNL) through several different mechanisms but only in a cursory fashion -- the libraries only guard against immediate calls evaluated by the OGNL engine via `SecurityMemberAccess`, but an allowed call that, instead, accepts nested arguments and, itself, invokes reflection internally executes outside of the...

Posted by Daniel Owens via Fulldisclosure on Nov 01Description The Apache Struts2 Spring Plugin opens a Spring `ApplicationContex` via a try-with-resources block and, outside of said block, then continues to use the closed resource, resulting in an uncaught `IllegalStateException`. This particular issue prevents proper functionality and indicates poor code quality and code review standards and processes, while not being, itself, otherwise excessively meaningful for a production environment...

Posted by Daniel Owens via Fulldisclosure on Nov 01As of the current versions of the Apache Struts2 JSON Plugin (e.g., version 7.4.0 and the 7.5.0 snapshot dated 28 October 2026), attackers can bypass the element-count limit purported to protect Object deserialisation added to said code as part of the WW-5618 and S2-072 "hardening controls". Please note that this vulnerability and the attack string is different than the previously reported bypass against the JSON array...

Posted by Daniel Owens via Fulldisclosure on Oct 28Summary Thus far we have written extensively about the rampant number of insecure JavaScript Object Notation (JSON) deserialisers available today, like in "Struts2 and Related Framework Array/Collection DoS" (26 October 2025) and "JSON Deserialiser Unconstrained Resource Consumption Quick Overview" (07 March 2026), along with a naïve proof of concept script that demonstrated what we were talking about -- "JSON...

Posted by Daniel Owens via Fulldisclosure on Oct 28Summary Thus far we have written extensively about the rampant number of insecure JavaScript Object Notation (JSON) deserialisers available today, like in "Struts2 and Related Framework Array/Collection DoS" (26 October 2025) and "JSON Deserialiser Unconstrained Resource Consumption Quick Overview" (07 March 2026), along with a naïve proof of concept script that demonstrated what we were talking about -- "JSON...

Posted by Daniel Owens via Fulldisclosure on Oct 28On 29 August 2026, we released "Commas of D00m" -- an old proof of concept that demonstrates unconstrained resource consumption in many JSON parsers. As recently discussed (in "Continued Apache Struts2 JSON Plugin Insecure Deserialisation"), the Apache Struts2 JSON Plugin's S2-072 and prior code changes fail to sufficiently protect against this style of attack. In that write-up, we examined the code and the...

Posted by Daniel Owens via Fulldisclosure on Oct 28On 29 August 2026, we released "Commas of D00m" -- an old proof of concept that demonstrates unconstrained resource consumption in many JSON parsers. As recently discussed (in "Continued Apache Struts2 JSON Plugin Insecure Deserialisation"), the Apache Struts2 JSON Plugin's S2-072 and prior code changes fail to sufficiently protect against this style of attack. In that write-up, we examined the code and the...

Posted by Daniel Owens via Fulldisclosure on Aug 29On 26 October 2025 we published "Struts2 and Related Framework Array/Collection DoS", which was followed up on 07 March 2026 by "JSON Deserialiser Unconstrained Resource Consumption Quick Overview". Today we are publishing a proof of concept that we have been using for more than 15 years against Struts2, Newtonsoft JSON, JSON.org, and various other JSON parsers. We are publishing, in part, because of the theft of our...

Apache Struts 2 vulnerability CVE-2024-53677, published in December 2024, exposed a severe flaw in the Struts2 file upload mechanism.