Description
In Tor before 0.3.3.12, 0.3.4.x before 0.3.4.11, 0.3.5.x before 0.3.5.8, and 0.4.x before 0.4.0.2-alpha, remote denial of service against Tor clients and relays can occur via memory exhaustion in the KIST cell scheduler.
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 | 0.3.5.8-1 | — |
| Debian 13 | tor | 0.3.5.8-1 | — |
| Debian 12 | tor | 0.3.5.8-1 | — |
Ubuntu
Security tracker ↗| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| Ubuntu Pro 20.04 LTS | tor | 0.4.2.7-1ubuntu0.1~esm1 | USN-5036-1 |
| Ubuntu Pro 18.04 LTS | tor | 0.3.2.10-1ubuntu0.2~esm1 | USN-5036-1 |
| Ubuntu Pro 16.04 LTS | tor | 0.2.9.14-1ubuntu1~16.04.3+esm1 | USN-5036-1 |
Show 1 more (older releases, extended support, other products)Fewer releases
| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| Ubuntu Pro 14.04 LTS | tor | 0.2.4.27-1ubuntu0.1+esm2 | USN-5036-1 |
SUSE
Security tracker ↗| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| SUSE Package Hub 15 | tor | 0.3.4.11-bp150.3.6.1 | openSUSE-SU-2019:1107-1 |
| SUSE Package Hub 12 | tor | 0.3.4.11-bp150.3.6.1 | openSUSE-SU-2019:1107-1 |
openSUSE
Security tracker ↗| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| openSUSE Tumbleweed | tor | 0.4.6.7-2.2 | openSUSE-SU-2024:11469-1 |
| openSUSE Leap 15.0 | tor | 0.3.4.11-bp150.3.6.1 | openSUSE-SU-2019:1107-1 |
Alpine
Security tracker ↗| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| Alpine v3.24 | tor | 0.3.5.8-r0 | — |
| Alpine v3.23 | tor | 0.3.5.8-r0 | — |
| Alpine v3.22 | tor | 0.3.5.8-r0 | — |
| Alpine v3.21 | tor | 0.3.5.8-r0 | — |
| Alpine v3.20 | tor | 0.3.5.8-r0 | — |
Show 12 more (older releases, extended support, other products)Fewer releases
| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| Alpine v3.19 | tor | 0.3.5.8-r0 | — |
| Alpine v3.18 | tor | 0.3.5.8-r0 | — |
| Alpine v3.17 | tor | 0.3.5.8-r0 | — |
| Alpine v3.16 | tor | 0.3.5.8-r0 | — |
| Alpine v3.15 | tor | 0.3.5.8-r0 | — |
| Alpine v3.14 | tor | 0.3.5.8-r0 | — |
| Alpine v3.13 | tor | 0.3.5.8-r0 | — |
| Alpine v3.12 | tor | 0.3.5.8-r0 | — |
| Alpine v3.11 | tor | 0.3.5.8-r0 | — |
| Alpine v3.10 | tor | 0.3.5.8-r0 | — |
| Alpine v3.9 | tor | 0.3.4.11-r0 | — |
| Alpine v3.8 | tor | 0.3.3.12-r0 | — |
Advisories 3
- USN-5036-1 tor vulnerabilities Ubuntu Security Notices (USN) · Jun 29, 2026
- openSUSE-SU-2024:11469-1 tor-0.4.6.7-2.2 on GA media SUSE / openSUSE Security Updates · Feb 4, 2026
- openSUSE-SU-2019:1107-1 Security update for tor SUSE / openSUSE Security Updates · Feb 4, 2026