Neo4j vulnerabilities

A vulnerability in Neo4j's Bolt modern handshake decoder treats an overlong capability bit mask the same as a truncated one. An unauthenticated client can send a selected protocol version with 32 continuation bytes, causing the decoder to reset the reader index and wait for more bytes instead of rejecting the message. The channel remains open, which can be exploited before authentication.

Insufficient escaping of unicode characters in query log in Neo4j Enterprise and Community editions prior to 2026.01 can lead to XSS if the user opens the logs in a tool that treats them as HTML. There is no security impact on Neo4j products, but this advisory is released as a precaution to treat the logs as plain text if using versions prior to 2026.01.

A potential information leak in the bolt protocol handshake in Neo4j Enterprise and Community editions allows an attacker to obtain one byte of information from previous connections. The attacker has no control over the information leaked in server responses.

The Cypher component in Neo4j 5.0.0 through 5.18 mishandles IMMUTABLE privileges in some situations where an attacker already has admin access.