Description
Tor before 0.2.4.23 and 0.2.5 before 0.2.5.6-alpha maintains a circuit after an inbound RELAY_EARLY cell is received by a client, which makes it easier for remote attackers to conduct traffic-confirmation attacks by using the pattern of RELAY and RELAY_EARLY cells as a means of communicating information about hidden service names.
Fixed in Linux distributions
Distributions backport fixes, so the version that fixes this vulnerability differs per release — upgrade to at least the version shown. From the distributions' security trackers and advisories.
Debian
Security tracker ↗| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| Debian 14 | tor | 0.2.4.23-1 | — |
| Debian 13 | tor | 0.2.4.23-1 | — |
| Debian 12 | tor | 0.2.4.23-1 | — |
| Debian 7 | tor | 0.2.4.23-1~deb7u1 | DSA-2993-1 |
| Debian 6.0 | tor | 0.2.4.23-1~deb6u1 | DLA-17-1 |
Ubuntu
Security tracker ↗| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| Ubuntu 14.04 LTS | tor | 0.2.4.27-1build0.14.04.1 | — |
openSUSE
Security tracker ↗| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| openSUSE Tumbleweed | tor | 0.2.8.11-1.1 | openSUSE-SU-2024:10423-1 |
Advisories 3
- DSA-2993-1 tor - security update Debian Security (DSA / DLA) · Mar 9, 2026
- DLA-17-1 tor - new upstream version Debian Security (DSA / DLA) · Mar 9, 2026
- openSUSE-SU-2024:10423-1 tor-0.2.8.11-1.1 on GA media SUSE / openSUSE Security Updates · Feb 4, 2026
References
- 60084 third-party-advisory
- https://trac.torproject.org/projects/tor/ticket/1038
- 60647 third-party-advisory
- https://blog.torproject.org/blog/tor-security-advisory-relay-early-traffic-confirmation-attack
- [tor-talk] 20140730 Tor 0.2.5.6-alpha is out mailing-list
- [tor-announce] 20140730 Tor security advisory: "relay early" traffic confirmation attack mailing-list
- [tor-announce] 20140730 Tor 0.2.4.23 is released mailing-list