Executive brief
Tor, the anonymity network software, contains a memory corruption vulnerability when processing cryptographic signatures with unexpected digest types. While most Tor users are minimally affected, directory authorities (which maintain the network's routing directory) could face significant disruption or data corruption, potentially affecting the stability and reliability of the entire Tor network.
Technical details
The vulnerability is an out-of-bounds write that occurs during parsing of consensus documents or detached signatures when an unexpected signature digest type is encountered. The flaw exists in signature validation logic and can result in memory corruption. Attack vectors include network delivery of malformed consensus data; directory authorities are at heightened risk due to their role in validating and relaying network consensus. The vulnerability is fixed in Tor 0.4.9.9 and later versions.
Affected products
- Tor Project Tor before 0.4.9.9
Timeline
- 2026-08-20: disclosed