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.

Affected: Ubuntu:Pro:14.04:LTS: tor, Ubuntu:Pro:16.04:LTS: tor, Ubuntu:Pro:18.04:LTS: tor, Ubuntu:Pro:20.04:LTS: tor

It was discovered that Tor incorrectly handled certain memory operations. A remote attacker could use this issue to cause a denial of service. This issue only affected Ubuntu 18.04 ESM. (CVE-2019-8955)

It was discovered that Tor did not properly handle the input length to dump_desc() function. A remote attacker could use this issue to cause a denial of service. This issue only affected Ubuntu 16.04 ESM, Ubuntu 18.04 ESM and Ubuntu 20.04 ESM. (CVE-2021-28089)

It was discovered that Tor did not properly sanitize the relay nickname in dirvote_add_signatures_to_pending_consensus() function. An attacker could possibly use this issue to cause an assertion failure and then cause a denial of service. (CVE-2021-28090)

It was discovered that Tor did not properly validate the layer hint on half-open streams. A remote attacker could possibly use this issue to bypass the access control, leading to remote code execution. This issue only affected Ubuntu 20.04 ESM. (CVE-2021-34548)

It was discovered that Tor was using an insecure hash function. A remote attacker could use this issue to cause a denial of service. This issue only affected Ubuntu 16.04 ESM, Ubuntu 18.04 ESM and Ubuntu 20.04 ESM. (CVE-2021-34549)

It was discovered that Tor did not properly manage memory under certain circumstances. If a user were tricked into opening a specially crafted request, a remote attacker could possibly use this issue to cause a crash, resulting in a denial of service, or possibly reading sensitive…