What is the CVSS score of CVE-2021-35331?

CVE-2021-35331 has a CVSS 3.1 base score of 7.8 (High). CVSS vector: CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H. EPSS exploitation probability: 1.6%.

Is there a public PoC exploit available for CVE-2021-35331?

Yes, a public proof-of-concept exploit is available for CVE-2021-35331. Prioritise patching immediately. EPSS: 1.6%.

Is there a patch available for CVE-2021-35331?

Yes, a patch is available for CVE-2021-35331. Update the affected software to the latest version immediately.

Tcl CVE-2021-35331

HIGH

Use of Externally-Controlled Format String (CWE-134)

2021-07-05 cve@mitre.org

RCE Tcl

7.8

CVSS 3.1 · NVD

View

Vulnerability Assessment

Weakness	CWE CWE-134 OWASP Top 10:2025 A05:2025 - Injection ASVS 5.0 V1 - Encoding and Sanitization Format string safety
Impact	CVSS score of 7.8 (HIGH). Attack characteristics: local attack vector, low complexity, no privileges required, user interaction required. Public proof-of-concept exploit code is available.
Exploit ScenarioDerived	Successful exploitation could compromise the high-severity affected system.

This Week Schedule remediation this week. Why: HIGH severity (CVSS 7.0-8.9).

Patch available 1.6% exploitation probability (EPSS)

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AnalysisAI

In Tcl 8.6.11, a format string vulnerability in nmakehlp.c might allow code execution via a crafted file. Rated high severity (CVSS 7.8), this vulnerability is no authentication required, low attack complexity. Public exploit code available.

RemediationAI

A vendor patch is available. Apply the latest security update as soon as possible. Apply vendor patches when available. Implement network segmentation and monitoring as interim mitigations.

Affects your stack

Find out whether the stacks and servers you run are on an affected version.

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 under CWE-134. In Tcl 8.6.11, a format string vulnerability in nmakehlp.c might allow code execution via a crafted file. NOTE: multiple third parties dispute the significance of this finding Affected products include: Tcl.

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Exploit and PoC references, threat intelligence from 22 sources

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Severity by source

NVD PRIMARY 7.8 HIGH

AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H

Primary rating from NVD · only source for this CVE.

CVSS VectorNVD

Attack Vector

Local

Attack Complexity

Low

Privileges Required

None

User Interaction

Required

Scope

Unchanged

Confidentiality

High

Integrity

High

Availability

High

DescriptionNVD

In Tcl 8.6.11, a format string vulnerability in nmakehlp.c might allow code execution via a crafted file. NOTE: multiple third parties dispute the significance of this finding

Threat Intelligence Overview

EPSS Score

1.6%

Top 26% exploitable

Exploit

POC

Public exploit code exists

Data Quality

3 sources

Confidence: Low

NVD

CVE.org

EPSS

GitHub

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.

SignalValue

Severity HIGH

CISA KEV No

Public POC Yes

EPSS 1.6%

Patch available Yes

Active threat No

Deciding rule

HIGH severity (CVSS 7.0-8.9)

What every action level means

Emergency Immediate action required. Criteria: CRITICAL + in CISA KEV (actively exploited) without patch, OR CRITICAL + EPSS > 30% without patch, OR CRITICAL + active threat signals without patch.

Act Now Prioritize within 24-48h. Criteria: in KEV with patch available, OR CRITICAL + public POC, OR HIGH + EPSS > 10%, OR CRITICAL + active threat, OR any CRITICAL severity.

This Week Schedule remediation this week. Criteria: HIGH severity (CVSS 7.0-8.9). Patch within normal change window.

This Month Plan within 30 days. Criteria: MEDIUM severity (CVSS 4.0-6.9), lower exploitation probability. Include in regular patch cycle.

Monitor Track and reassess. Criteria: LOW severity (CVSS 0.1-3.9), minimal exploitation risk. No immediate action needed.

SSVC AssessmentENISA

SSVC Decision· derived

Scheduled

Exploitation· derived

Poc

System Exposure· derived

Small

Automatable· derived

Human Impact· derived

Medium

Priority Score

Low Medium High Critical

KEV: 0

EPSS: +2

CVSS: +39

PoC: +20

Weaponized: 0

Threat intel: 0

Gov advisory: 0

Attack Technique

Remote Code Execution CRITICAL

Remote Code Execution represents the critical moment when an attacker successfully runs arbitrary code on a target system without physical access.

Affected Products (CPE)NVD

cpe:2.3:a:tcl:tcl:8.6.11:*:*:*:*:*:*:*

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