In plain words
Imagine you have a safe where important papers are kept, and this safe has a special lock that checks if the papers have been tampered with. But sometimes, because of a problem with the lock, it stops checking if the papers are authentic after someone tries to open it in a certain way. This is similar to what is happening with Apache WSS4J, a tool used to secure web services, where a flaw allows signature checks to be skipped under specific conditions.
What's broken
The bug, known as CVE-2026-92121¹, affects versions of Apache WSS4J before 4.0.2, 3.0.6, and 2.4.4. An attacker could potentially exploit this to tamper with the security of web services without being detected, as the signature checks are skipped after an STR-Transform reference² in the streaming code.
How it actually works
Here's how it works: when Apache WSS4J is used with the WS-SecurityPolicy³, it is supposed to check the signatures of messages to ensure they have not been tampered with. However, due to this flaw, if a message includes an STR-Transform reference, the internal flag that tracks whether the content is signed or not gets stuck as 'inside signed content', causing subsequent signature checks to be skipped. This means an attacker could manipulate messages without the system detecting the changes, as the signature verification⁴ process is bypassed.
Proof of concept
A proof of concept⁵ (PoC) would demonstrate that this flaw can be exploited to bypass signature checks, showing that the vulnerability is real and not just theoretical. The existence of a PoC would increase the urgency for users to update their Apache WSS4J versions, as it would provide a tangible example of how the vulnerability could be exploited. However, it is not clear from the source if a public PoC exists.
Is it real
It is not specified in the provided information whether this vulnerability is being actively exploited in the wild. Limiting factors could include the need for specific conditions to be met, such as the use of STR-Transform references in the streaming code. Users of affected versions should update to the latest version of Apache WSS4J to mitigate this vulnerability.
What to do
To fix this issue, users should update Apache WSS4J to a version that is not affected by this vulnerability, such as version 4.0.2 or later for the 4.0 series, 3.0.6 or later for the 3.0 series, and 2.4.4 or later for versions before 3.0. This update will ensure that the signature checks are properly performed, even after an STR-Transform reference is encountered.
Terms
- ¹ CVE-2026-92121
- , A unique identifier for a security vulnerability
- ² STR-Transform
- , A transformation reference used in WS-Security that can affect how messages are processed
- ³ WS-SecurityPolicy
- , A policy for securing web services that includes specifications for message security
- ⁴ signature verification
- , The process of verifying that a message has not been tampered with by checking its digital signature
- ⁵ proof of concept
- , A demonstration that a security vulnerability can be exploited, proving it is not just theoretical