Tor before 0.4.9.7 contains an out-of-bounds read by one byte when processing a malformed BEGIN cell. This leads to a small memory disclosure that could leak adjacent data but does not alter program state or permit code execution. The weakness is identified as a one-byte read beyond buffer boundaries (CWE-193).

The vulnerability affects all installations of Tor older than 0.4.9.7. No other vendors or products are listed. Users running earlier Tor versions should check the upgrade status.

The CVSS score of 3.7 classifies the issue as low severity. The EPSS score is unavailable, and the vulnerability is not currently listed in CISA's KEV catalog. Attack vectors are inferred to include delivery of malformed cells over the Tor circuit, which may be possible from a remote network actor with control over cell injection. Exploitation would only enable data exposure on the affected node, and no evidence of privilege escalation or persistence is reported.