Description
tor before 0.4.9.9 was prone to a NULL write after free when sending a CONFLUX_SWITCH cell fails. The return value of relay_send_command_from_edge() was ignored, so a send failure (which calls circuit_mark_for_close() and removes the leg via cfx_del_leg()) would go undetected, causing the caller to write to the now-freed current leg and resulting in a crash. This is TROVE-2026-017.
Affected products
| Vendor | Product | Affected | Fixed |
|---|---|---|---|
| torproject | Tor | 0.4.8.1-alpha – < 0.4.9.9 | 0.4.9.9 |
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 | 0.4.9.9-1 | — |
| Debian 13 | tor | 0.4.9.11-0+deb13u1 | — |
| Debian 12 | tor | 0.4.9.9-1 | — |
Ubuntu
Security tracker ↗| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| Ubuntu 26.04 LTS | tor | No fix yet | — |
| Ubuntu 24.04 LTS | tor | No fix yet | — |
| Ubuntu 22.04 LTS | tor | No fix yet | — |
Show 4 more (older releases, extended support, other products)Fewer releases
| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| Ubuntu Pro 20.04 LTS | tor | No fix yet | — |
| Ubuntu Pro 18.04 LTS | tor | No fix yet | — |
| Ubuntu Pro 16.04 LTS | tor | No fix yet | — |
| Ubuntu Pro 14.04 LTS | tor | No fix yet | — |
Advisories 1
- WID-SEC-2026-2959 Tor: Mehrere Schwachstellen BSI CERT-Bund (WID) · Aug 30, 2026