CVE-2025-4444VulnerabilityPublished 18 Sep 2025

CVE-2025-4444: Tor · Resource Consumption

Affects TorSource CVE Database V5

Not known to be exploited · CVSS 6.3 Medium.

Data as of 25 Oct 2026, 19:02 UTC

CVSS 4.0 base score

6.3Medium

How severe the flaw is on the 0–10 CVSS scale.

EPSS: 0.4% chance of exploitation in 30 days – higher than 40% of CVEsExploit Prediction Scoring System: the likelihood attackers will use this flaw soon.

CVSS:4.0/AV:N/AC:H/AT:N/PR:N/UI:N/VC:N/VI:N/VA:L/SC:N/SI:N/SA:N/E:X

Attack Vector: Network
Attack Complexity: High
Attack Requirements: None
Privileges Required: None
User Interaction: None
Vulnerable system confidentiality: None
Vulnerable system integrity: None
Vulnerable system availability: Low
Subsequent system confidentiality: None
Subsequent system integrity: None
Subsequent system availability: None

Bold values are the worst case: easiest to exploit or largest impact.

Attack Vector: Network: The vulnerable system is bound to the network stack and the set of possible attackers extends beyond the other options listed below, up to and including the entire Internet. Such a vulnerability is often termed “remotely exploitable” and can be thought of as an attack being exploitable at the protocol level one or more network hops away (e.g., across one or more routers).
Attack Complexity: High: The successful attack depends on the evasion or circumvention of security-enhancing techniques in place that would otherwise hinder the attack. These include: Evasion of exploit mitigation techniques, for example, circumvention of address space randomization (ASLR) or data execution prevention (DEP) must be performed for the attack to be successful; Obtaining target-specific secrets. The attacker must gather some target-specific secret before the attack can be successful. A secret is any piece of information that cannot be obtained through any amount of reconnaissance. To obtain the secret the attacker must perform additional attacks or break otherwise secure measures (e.g. knowledge of a secret key may be needed to break a crypto channel). This operation must be performed for each attacked target.
Attack Requirements: None: The successful attack does not depend on the deployment and execution conditions of the vulnerable system. The attacker can expect to be able to reach the vulnerability and execute the exploit under all or most instances of the vulnerability.
Privileges Required: None: The attacker is unauthorized prior to attack, and therefore does not require any access to settings or files of the vulnerable system to carry out an attack.
User Interaction: None: The vulnerable system can be exploited without interaction from any human user, other than the attacker.
Vulnerable system confidentiality: None: There is no loss of confidentiality within the Vulnerable System.
Vulnerable system integrity: None: There is no loss of integrity within the Vulnerable System.
Vulnerable system availability: Low: Performance is reduced or there are interruptions in resource availability. Even if repeated exploitation of the vulnerability is possible, the attacker does not have the ability to completely deny service to legitimate users. The resources in the Vulnerable System are either partially available all of the time, or fully available only some of the time, but overall there is no direct, serious consequence to the Vulnerable System.
Subsequent system confidentiality: None: There is no loss of confidentiality within the Subsequent System or all confidentiality impact is constrained to the Vulnerable System.
Subsequent system integrity: None: There is no loss of integrity within the Subsequent System or all integrity impact is constrained to the Vulnerable System.
Subsequent system availability: None: There is no impact to availability within the Subsequent System or all availability impact is constrained to the Vulnerable System.

Definitions: FIRST CVSS v4.0 specification.

Exploitation evidence

Disclosed: evidence found.
CVE published 18 Sep 2025
Detectable: no evidence on record.
No public nuclei template indexed
Weaponised: no evidence on record.
No public exploit code indexed in Metasploit or Exploit-DB
Exploited in the wildExploited: no evidence on record.
Not in CISA KEV and no source reports exploitation
Observed by OffSeq MirageSeen by Mirage: no evidence on record.
No attack traffic recorded by OffSeq Mirage sensors

A missing step is not evidence of safety. Sources: cve.org (opens in a new tab), the Metasploit, Exploit-DB and nuclei-templates index as of 2026-10-25.

Disclosed: The CVE record is public on cve.org. Its publication is t = 0.
Detectable: A public nuclei template can find exposed instances, for defenders and attackers alike.
Weaponised: Public exploit code exists in Metasploit or Exploit-DB, or CISA SSVC reports a public proof of concept.
Exploited in the wild: CISA KEV lists it, CISA SSVC rates exploitation active, or a source reports attacks.
Observed by OffSeq Mirage: OffSeq Mirage honeypot sensors recorded attack traffic for this CVE, or found exposed hosts without attack traffic.

Moments are spaced evenly, not to scale; a dashed line marks a gap of six months or more. Deltas count from t = 0. Sources that give only a date (CISA KEV, Exploit-DB, or a time of exactly 00:00Z) read “same day” rather than hours. Metasploit modules carry the flaw’s disclosure date, not their release date, and nuclei templates carry no date, so both appear above but not on the timeline.

What to do

Affected software

Product	Affected	Fixed in
Tor	Affected =0.4.7.0 =0.4.7.1 =0.4.7.2 =0.4.7.3 =0.4.7.4 =0.4.7.5 =0.4.7.6 =0.4.7.7 =0.4.7.8 =0.4.7.9 =0.4.7.10 =0.4.7.11 =0.4.7.12 =0.4.7.13 =0.4.7.14 =0.4.7.15 =0.4.7.16 =0.4.8.0 =0.4.8.1 =0.4.8.2 =0.4.8.3 =0.4.8.4 =0.4.8.5 =0.4.8.6 =0.4.8.7 =0.4.8.8 =0.4.8.9 =0.4.8.10 =0.4.8.11 =0.4.8.12 =0.4.8.13 =0.4.8.14 =0.4.8.15 =0.4.8.16 =0.4.8.17	Fixed in–

AI-suggested

European organizations should prioritize upgrading all Tor instances to versions 0.4.8.18 or later, including the 0.4.9.3-alpha release, to remediate this vulnerability. Network administrators should audit their Tor deployments to identify affected versions and apply patches promptly. Additionally, monitoring resource usage on Tor nodes and onion services can help detect anomalous spikes indicative of exploitation attempts. Implementing rate limiting or resource allocation controls on the Onion Service Descriptor Handler may mitigate the impact of resource consumption attacks. Organizations operating critical onion services should consider deploying redundant nodes and load balancing to maintain availability during potential attack attempts. Regularly reviewing Tor project advisories and subscribing to vulnerability feeds will ensure timely awareness of emerging threats. Finally, restricting access to Tor nodes through network segmentation or firewall rules where feasible can reduce exposure to remote exploitation attempts.

Description

A security flaw has been discovered in Tor up to 0.4.7.16/0.4.8.17. Impacted is an unknown function of the component Onion Service Descriptor Handler. Performing manipulation results in resource consumption. The attack may be initiated remotely. The attack's complexity is rated as high. The exploitability is considered difficult. Upgrading to version 0.4.8.18 and 0.4.9.3-alpha is recommended to address this issue. It is recommended to upgrade the affected component.

Impact

For European organizations, the impact of CVE-2025-4444 could be significant in contexts where Tor is used to ensure privacy, circumvent censorship, or provide anonymous services. Organizations running onion services for secure communications, whistleblowing platforms, or privacy-focused applications may experience service disruptions or degraded performance due to resource exhaustion attacks exploiting this vulnerability. This could lead to temporary denial of service, impacting availability and potentially undermining trust in privacy-preserving infrastructure. Additionally, entities relying on Tor for secure browsing or communication may face increased latency or connection failures. While the vulnerability does not directly compromise confidentiality or integrity, the availability impact can hinder critical operations, especially for NGOs, journalists, or activists in Europe who depend on Tor for secure communication. The medium severity and high attack complexity suggest that widespread exploitation is less likely but targeted attacks against high-value onion services remain a concern.

References

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Exploitation evidence

What to do

Affected software

Description

AI analysisMachine-generated, updated 18 Sep 2025, 14:03 UTC

Technical details

References

Community reviews

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