CVE-2021-20201Public exploitNetwork attack vector

CPU exhaustion via unrestricted TLS renegotiation

Published May 28, 2021 · Updated Aug 3, 2024

Denial of service in SPICE Server before 0.14.92 allows remote attackers to exhaust server CPU through repeated TLS renegotiation. The server's TLS setup accepts client-initiated renegotiation on one connection, repeatedly invoking expensive cryptographic handshake work without limiting requests. No authentication or user interaction is required; a reachable TLS-enabled endpoint can become unresponsive through CPU saturation, without reported data disclosure or modification.

CVSS severity5.3
Medium
EPSS probability2.70%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Denial of service in SPICE Server before 0.14.92 allows remote attackers to exhaust server CPU through repeated TLS renegotiation. The server's TLS setup accepts client-initiated renegotiation on one connection, repeatedly invoking expensive cryptographic handshake work without limiting requests. No authentication or user interaction is required; a reachable TLS-enabled endpoint can become unresponsive through CPU saturation, without reported data disclosure or modification.

The record

CVE
CVE-2021-20201
Published
May 28, 2021
Updated
Aug 3, 2024
Vendor
SPICE
Product
SPICE Server
Classifications
CWE-400, T1499.002
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. May 28, 2021CVE publishedPublication date reported by the CVE source.
  2. Aug 3, 2024Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=spice 0.14.92

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

SPICE · SPICE Serverversion=spice 0.14.92

Published CVSS scores

5.3CanonicalCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

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No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitPublished

Weakness, pattern, technique

CWE-400Uncontrolled Resource Consumption
T1499.002Endpoint Denial of Service: Service Exhaustion Flood

Public exploit references

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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