In plain words
Imagine you have a mailbox where you receive letters, but someone can send you a letter with a ridiculously large address label that makes your mailbox overflow and stop working. This is similar to what happens with the Apache WSS4J security flaw, where an attacker can send a special kind of message that makes the system crash due to an integer overflow¹ in how it handles X.509 certificate extensions².
What's broken
The bug is in Apache WSS4J, specifically in how it checks the size of certain parts of X.509 certificates³. An attacker can send a message with a certificate that claims to have an extremely large size, which WSS4J does not properly validate, leading to a crash. The affected versions are Apache WSS4J 4.0.0 before 4.0.2, Apache WSS4J 3.0.0 before 3.0.6, and Apache WSS4J before 2.4.4. This vulnerability has a CVE id of CVE-2026-95616⁴.
How it actually works
Here's how it works: when WSS4J receives a SOAP message with an X.509 certificate, it tries to parse the certificate's extensions. If the certificate's SubjectKeyIdentifier extension claims to have a length of 0x7FFFFFFF, WSS4J's DER⁵ bounds check fails to stop it, allowing an oversized allocation that crashes the system. This happens because WSS4J does not correctly handle the integer overflow⁶ when checking the size of the extension.
Proof of concept
There is a public proof-of-concept⁷ that demonstrates this vulnerability. A proof-of-concept shows that the flaw is real and can be exploited, making it more urgent to patch. The existence of a public proof-of-concept means that attackers can more easily find and exploit this vulnerability, which is why it's important to update Apache WSS4J to a fixed version.
Is it real
It is not clear from the source if this vulnerability is being actively exploited in the wild. However, the fact that it can be exploited without authentication⁸ and affects multiple versions of Apache WSS4J makes it a significant concern. The limiting factor is that an attacker needs to send a specially crafted SOAP message to exploit this vulnerability.
What to do
To fix this vulnerability, you should update Apache WSS4J to version 4.0.2 or later, version 3.0.6 or later, or version 2.4.4 or later, depending on which branch you are using. This will patch the integer overflow bug and prevent attackers from crashing your system with a specially crafted message.
Terms
- ¹ integer overflow
- , An integer overflow occurs when a computer tries to store a number that is too large for its memory, causing it to wrap around and become a very small or negative number.
- ² X.509 certificate
- , X.509 certificates are digital certificates that verify the identity of a user, computer, or organization, and are used for secure communication over the internet.
- ³ DER
- , A DER is a way of encoding data, like a set of instructions, that computers can understand.
- ⁴ CVE
- , A CVE, or Common Vulnerabilities and Exposures, is a list of publicly known cybersecurity vulnerabilities and exposures.
- ⁵ DER parsing
- , DER parsing refers to the process of decoding and interpreting the data encoded in DER format.