Tor
CVE-2021-28089
HIGH
Vulnerability Assessment
| Weakness |
CWE
OWASP Top 10:2025
A06:2025 - Insecure Design
ASVS 5.0
V2 - Validation and Business Logic Resource consumption limits
MITRE ATT&CK
1 technique across 1 tactic: Impact The technique list with ATT&CK links and the kill-chain view is part of the Basic plan and up. |
| Impact | CVSS score of 7.5 (HIGH). Attack characteristics: network attack vector, low complexity, no privileges required, no user interaction not required. |
| Exploit ScenarioDerived | A remote attacker could cause denial of service by exhausting system resources by sending crafted requests to the affected application. No authentication is required to exploit this vulnerability. |
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Alert meAnalysisAI
Tor before 0.4.5.7 allows a remote participant in the Tor directory protocol to exhaust CPU resources on a target, aka TROVE-2021-001. Rated high severity (CVSS 7.5), this vulnerability is remotely exploitable, no authentication required, low attack complexity. No vendor patch available.
RemediationAI
No vendor patch is available at time of analysis. Monitor vendor advisories for updates. Implement rate limiting, set resource quotas, validate input sizes, use timeouts.
Affects your stack
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Checking this CVE against your own stacks and servers is part of the Basic plan and up.
Technical ContextAI · show details
This vulnerability is classified as Uncontrolled Resource Consumption (CWE-400), which allows attackers to cause denial of service by exhausting system resources. Tor before 0.4.5.7 allows a remote participant in the Tor directory protocol to exhaust CPU resources on a target, aka TROVE-2021-001. Affected products include: Torproject Tor, Fedoraproject Fedora. Version information: before 0.4.5.7.
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Severity by source
AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
Primary rating from NVD · only source for this CVE.
CVSS VectorNVD
DescriptionNVD
Tor before 0.4.5.7 allows a remote participant in the Tor directory protocol to exhaust CPU resources on a target, aka TROVE-2021-001.
Threat Intelligence Overview
NVD
CVE.org
EPSS
How this decision was reached
The engine reads each signal below and applies a fixed list of rules from top to bottom. The first rule that matches sets the recommended action – like a statement, every line is shown.
What every action level means
SSVC AssessmentENISA
Priority Score
Attack Technique
Denial of Service attacks render applications or systems unavailable by overwhelming resources or triggering failure conditions.
Affected Products (CPE)NVD
Tor Browser before 7.0.9 on macOS and Linux allows remote attackers to bypass the intended anonymity feature and discove
Tor before 0.3.5.16, 0.4.5.10, and 0.4.6.7 mishandles the relationship between batch-signature verification and single-s
A use-after-free issue was discovered in Tor 0.3.2.x before 0.3.2.10. Rated high severity (CVSS 7.5), this vulnerability
The SafeSocks option in Tor before 0.4.7.13 has a logic error in which the unsafe SOCKS4 protocol can be used but not th
Out-of-bounds write in The Tor Project's tor daemon (0.2.8.2-alpha through versions before 0.4.9.9) can be triggered whe
The daemon in Tor through 0.4.1.8 and 0.4.2.x through 0.4.2.6 does not verify that a rendezvous node is known before att
Out-of-bounds read by one byte in Tor before version 0.4.9.7 when processing malformed BEGIN cells allows remote unauthe
An out-of-bounds read in Tor before 0.4.9.7 can be triggered by a malicious circuit participant sending an END, TRUNCATE
Rendezvous-point impersonation in Tor before 0.4.9.11 lets a malicious relay that a client happens to select as its rend
Write-after-free in Tor's conflux (traffic-splitting) subsystem allows a remote unauthenticated attacker to crash a Tor
Use-after-free in Tor's conflux circuit handling allows a malicious Tor client to corrupt relay memory by sending a RELA
In Tor before 0.2.5.16, 0.2.6 through 0.2.8 before 0.2.8.17, 0.2.9 before 0.2.9.14, 0.3.0 before 0.3.0.13, and 0.3.1 bef
GitHub PoC
Exploit-DB