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Vulnerability details: VCID-zgsu-4k3d-93h2
Vulnerability ID VCID-zgsu-4k3d-93h2
Aliases CVE-2021-43854
GHSA-f8m6-h2c7-8h9x
PYSEC-2021-859
Summary Inefficient Regular Expression Complexity in nltk (word_tokenize, sent_tokenize)
Status Published
Exploitability 0.5
Weighted Severity 8.0
Risk 4.0
Affected and Fixed Packages Package Details
Weaknesses (3)
CWE-400 Uncontrolled Resource Consumption
CWE-937 OWASP Top Ten 2013 Category A9 - Using Components with Known Vulnerabilities
CWE-1035 OWASP Top Ten 2017 Category A9 - Using Components with Known Vulnerabilities
System Score Found at
epss 0.00144 https://api.first.org/data/v1/epss?cve=CVE-2021-43854
epss 0.00144 https://api.first.org/data/v1/epss?cve=CVE-2021-43854
epss 0.00144 https://api.first.org/data/v1/epss?cve=CVE-2021-43854
epss 0.00144 https://api.first.org/data/v1/epss?cve=CVE-2021-43854
cvssv3.1_qr HIGH https://github.com/advisories/GHSA-f8m6-h2c7-8h9x
cvssv3.1 7.5 https://github.com/nltk/nltk
cvssv4 8.7 https://github.com/nltk/nltk
generic_textual HIGH https://github.com/nltk/nltk
cvssv3.1 7.5 https://github.com/nltk/nltk/commit/1405aad979c6b8080dbbc8e0858f89b2e3690341
cvssv4 8.7 https://github.com/nltk/nltk/commit/1405aad979c6b8080dbbc8e0858f89b2e3690341
generic_textual HIGH https://github.com/nltk/nltk/commit/1405aad979c6b8080dbbc8e0858f89b2e3690341
cvssv3.1 7.5 https://github.com/nltk/nltk/issues/2866
cvssv4 8.7 https://github.com/nltk/nltk/issues/2866
generic_textual HIGH https://github.com/nltk/nltk/issues/2866
cvssv3.1 7.5 https://github.com/nltk/nltk/pull/2869
cvssv4 8.7 https://github.com/nltk/nltk/pull/2869
generic_textual HIGH https://github.com/nltk/nltk/pull/2869
cvssv3.1 7.5 https://github.com/nltk/nltk/security/advisories/GHSA-f8m6-h2c7-8h9x
cvssv3.1_qr HIGH https://github.com/nltk/nltk/security/advisories/GHSA-f8m6-h2c7-8h9x
cvssv4 8.7 https://github.com/nltk/nltk/security/advisories/GHSA-f8m6-h2c7-8h9x
generic_textual HIGH https://github.com/nltk/nltk/security/advisories/GHSA-f8m6-h2c7-8h9x
cvssv3.1 7.5 https://github.com/pypa/advisory-database/tree/main/vulns/nltk/PYSEC-2021-859.yaml
cvssv4 8.7 https://github.com/pypa/advisory-database/tree/main/vulns/nltk/PYSEC-2021-859.yaml
generic_textual HIGH https://github.com/pypa/advisory-database/tree/main/vulns/nltk/PYSEC-2021-859.yaml
cvssv3.1 7.5 https://nvd.nist.gov/vuln/detail/CVE-2021-43854
cvssv4 8.7 https://nvd.nist.gov/vuln/detail/CVE-2021-43854
generic_textual HIGH https://nvd.nist.gov/vuln/detail/CVE-2021-43854
Reference id Reference type URL
https://api.first.org/data/v1/epss?cve=CVE-2021-43854
https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2021-43854
https://github.com/nltk/nltk
https://github.com/nltk/nltk/commit/1405aad979c6b8080dbbc8e0858f89b2e3690341
https://github.com/nltk/nltk/issues/2866
https://github.com/nltk/nltk/pull/2869
https://github.com/pypa/advisory-database/tree/main/vulns/nltk/PYSEC-2021-859.yaml
1002623 https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=1002623
CVE-2021-43854 https://nvd.nist.gov/vuln/detail/CVE-2021-43854
GHSA-f8m6-h2c7-8h9x https://github.com/advisories/GHSA-f8m6-h2c7-8h9x
GHSA-f8m6-h2c7-8h9x https://github.com/nltk/nltk/security/advisories/GHSA-f8m6-h2c7-8h9x
USN-7365-1 https://usn.ubuntu.com/7365-1/
No exploits are available.
Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H Found at https://github.com/nltk/nltk
Attack Vector (AV) Attack Complexity (AC) Privileges Required (PR) User Interaction (UI) Scope (S) Confidentiality Impact (C) Integrity Impact (I) Availability Impact (A)

network

adjacent_network

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physical

low

high

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unchanged

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Vector: CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N Found at https://github.com/nltk/nltk
Attack Vector (AV) Attack Complexity (AC) Attack Requirements (AT) Privileges Required (PR) User Interaction (UI) Vulnerable System Impact Confidentiality (VC) Vulnerable System Impact Integrity (VI) Vulnerable System Impact Availability (VA) Subsequent System Impact Confidentiality (SC) Subsequent System Impact Integrity (SI) Subsequent System Impact Availability (SA)

network

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Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H Found at https://github.com/nltk/nltk/commit/1405aad979c6b8080dbbc8e0858f89b2e3690341
Attack Vector (AV) Attack Complexity (AC) Privileges Required (PR) User Interaction (UI) Scope (S) Confidentiality Impact (C) Integrity Impact (I) Availability Impact (A)

network

adjacent_network

local

physical

low

high

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required

unchanged

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Vector: CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N Found at https://github.com/nltk/nltk/commit/1405aad979c6b8080dbbc8e0858f89b2e3690341
Attack Vector (AV) Attack Complexity (AC) Attack Requirements (AT) Privileges Required (PR) User Interaction (UI) Vulnerable System Impact Confidentiality (VC) Vulnerable System Impact Integrity (VI) Vulnerable System Impact Availability (VA) Subsequent System Impact Confidentiality (SC) Subsequent System Impact Integrity (SI) Subsequent System Impact Availability (SA)

network

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passive

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Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H Found at https://github.com/nltk/nltk/issues/2866
Attack Vector (AV) Attack Complexity (AC) Privileges Required (PR) User Interaction (UI) Scope (S) Confidentiality Impact (C) Integrity Impact (I) Availability Impact (A)

network

adjacent_network

local

physical

low

high

none

low

high

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required

unchanged

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Vector: CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N Found at https://github.com/nltk/nltk/issues/2866
Attack Vector (AV) Attack Complexity (AC) Attack Requirements (AT) Privileges Required (PR) User Interaction (UI) Vulnerable System Impact Confidentiality (VC) Vulnerable System Impact Integrity (VI) Vulnerable System Impact Availability (VA) Subsequent System Impact Confidentiality (SC) Subsequent System Impact Integrity (SI) Subsequent System Impact Availability (SA)

network

adjacent

local

physical

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present

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passive

active

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Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H Found at https://github.com/nltk/nltk/pull/2869
Attack Vector (AV) Attack Complexity (AC) Privileges Required (PR) User Interaction (UI) Scope (S) Confidentiality Impact (C) Integrity Impact (I) Availability Impact (A)

network

adjacent_network

local

physical

low

high

none

low

high

none

required

unchanged

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Vector: CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N Found at https://github.com/nltk/nltk/pull/2869
Attack Vector (AV) Attack Complexity (AC) Attack Requirements (AT) Privileges Required (PR) User Interaction (UI) Vulnerable System Impact Confidentiality (VC) Vulnerable System Impact Integrity (VI) Vulnerable System Impact Availability (VA) Subsequent System Impact Confidentiality (SC) Subsequent System Impact Integrity (SI) Subsequent System Impact Availability (SA)

network

adjacent

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physical

low

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passive

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Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H Found at https://github.com/nltk/nltk/security/advisories/GHSA-f8m6-h2c7-8h9x
Attack Vector (AV) Attack Complexity (AC) Privileges Required (PR) User Interaction (UI) Scope (S) Confidentiality Impact (C) Integrity Impact (I) Availability Impact (A)

network

adjacent_network

local

physical

low

high

none

low

high

none

required

unchanged

changed

high

low

none

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Vector: CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N Found at https://github.com/nltk/nltk/security/advisories/GHSA-f8m6-h2c7-8h9x
Attack Vector (AV) Attack Complexity (AC) Attack Requirements (AT) Privileges Required (PR) User Interaction (UI) Vulnerable System Impact Confidentiality (VC) Vulnerable System Impact Integrity (VI) Vulnerable System Impact Availability (VA) Subsequent System Impact Confidentiality (SC) Subsequent System Impact Integrity (SI) Subsequent System Impact Availability (SA)

network

adjacent

local

physical

low

high

none

present

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passive

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Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H Found at https://github.com/pypa/advisory-database/tree/main/vulns/nltk/PYSEC-2021-859.yaml
Attack Vector (AV) Attack Complexity (AC) Privileges Required (PR) User Interaction (UI) Scope (S) Confidentiality Impact (C) Integrity Impact (I) Availability Impact (A)

network

adjacent_network

local

physical

low

high

none

low

high

none

required

unchanged

changed

high

low

none

high

low

none

high

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none
Vector: CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N Found at https://github.com/pypa/advisory-database/tree/main/vulns/nltk/PYSEC-2021-859.yaml
Attack Vector (AV) Attack Complexity (AC) Attack Requirements (AT) Privileges Required (PR) User Interaction (UI) Vulnerable System Impact Confidentiality (VC) Vulnerable System Impact Integrity (VI) Vulnerable System Impact Availability (VA) Subsequent System Impact Confidentiality (SC) Subsequent System Impact Integrity (SI) Subsequent System Impact Availability (SA)

network

adjacent

local

physical

low

high

none

present

none

low

high

none

passive

active

high

low

none

high

low

none

high

low

none

high

low

none

high

low

none

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low

none
Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H Found at https://nvd.nist.gov/vuln/detail/CVE-2021-43854
Attack Vector (AV) Attack Complexity (AC) Privileges Required (PR) User Interaction (UI) Scope (S) Confidentiality Impact (C) Integrity Impact (I) Availability Impact (A)

network

adjacent_network

local

physical

low

high

none

low

high

none

required

unchanged

changed

high

low

none

high

low

none

high

low

none
Vector: CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N Found at https://nvd.nist.gov/vuln/detail/CVE-2021-43854
Attack Vector (AV) Attack Complexity (AC) Attack Requirements (AT) Privileges Required (PR) User Interaction (UI) Vulnerable System Impact Confidentiality (VC) Vulnerable System Impact Integrity (VI) Vulnerable System Impact Availability (VA) Subsequent System Impact Confidentiality (SC) Subsequent System Impact Integrity (SI) Subsequent System Impact Availability (SA)

network

adjacent

local

physical

low

high

none

present

none

low

high

none

passive

active

high

low

none

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none

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Exploit Prediction Scoring System (EPSS)
Percentile 0.3453
EPSS Score 0.00144
Published At June 11, 2026, 12:55 p.m.
Date Actor Action Source VulnerableCode Version
2026-06-11T20:27:24.555466+00:00 GHSA Importer Import https://github.com/advisories/GHSA-f8m6-h2c7-8h9x 38.6.0