Tor ships back-to-back security releases 0.4.9.12 and 0.4.9.13, fixing high-severity flaws including undetectable guard-led circuit tampering

Tor Project urges immediate upgrades: 0.4.9.12 fixes a flaw letting a malicious guard steer circuit building to attacker-chosen relays undetected, while 0.4.9.13 (released 2026-09-23) ships several more high-severity fixes for relays, clients, and onion…

Two Tor Project security releases were forwarded to the oss-security mailing list on 2026-09-24. Sam James highlighted release 0.4.9.12, whose most significant fix addresses a circuit-building flaw: a malicious guard relay can influence which relays a circuit uses, and Tor does not detect the tampering — directly undermining Tor's path-selection and anonymity guarantees. That post cites no CVE identifier and reports no active exploitation. The second post forwards Tor Project security release 0.4.9.13, issued 2026-09-23, which contains several high-severity fixes affecting all major Tor components — relays, clients, and onion services. The 0.4.9.13 fixes are described as largely originating from an LLM-generated report pipeline, and Tor strongly recommends upgrading as soon as possible; no CVE identifiers appear in the forwarded excerpt. The two reports are complementary and do not conflict.

• Tor security release 0.4.9.12 fixes a circuit-building flaw: a malicious guard can steer circuits toward relays of its choosing, and Tor does not detect the tampering.
• The 0.4.9.12 flaw post cites no CVE identifier and reports no active exploitation.
• Tor security release 0.4.9.13 was issued on 2026-09-23 and ships several high-severity security fixes.
• The 0.4.9.13 fixes affect relays, clients, and onion services alike.
• The 0.4.9.13 fixes are described as largely originating from an LLM-generated report pipeline.
• No CVE identifiers are listed in the forwarded 0.4.9.13 excerpt.
• Tor Project strongly recommends upgrading to the latest release as soon as possible.
• Both releases were discussed on oss-security on 2026-09-24 (posts at 06:07:33Z and 06:11:14Z); the 0.4.9.12 post was by Sam James.