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Vulnerability details: VCID-3mxv-vxtj-8kde
Vulnerability ID VCID-3mxv-vxtj-8kde
Aliases CVE-2026-21860
GHSA-87hc-h4r5-73f7
Summary Werkzeug safe_join() allows Windows special device names with compound extensions Werkzeug's `safe_join` function allows path segments with Windows device names that have file extensions or trailing spaces. On Windows, there are special device names such as `CON`, `AUX`, etc that are implicitly present and readable in every directory. Windows still accepts them with any file extension, such as `CON.txt`, or trailing spaces such as `CON `. This was previously reported as https://github.com/pallets/werkzeug/security/advisories/GHSA-hgf8-39gv-g3f2, but the fix failed to account for compound extensions such as `CON.txt.html` or trailing spaces. It also missed some additional special names. `send_from_directory` uses `safe_join` to safely serve files at user-specified paths under a directory. If the application is running on Windows, and the requested path ends with a special device name, the file will be opened successfully, but reading will hang indefinitely.
Status Published
Exploitability 0.5
Weighted Severity 6.2
Risk 3.1
Affected and Fixed Packages Package Details
Weaknesses (3)
CWE-67 Improper Handling of Windows Device Names
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 0.00022 https://api.first.org/data/v1/epss?cve=CVE-2026-21860
epss 0.00022 https://api.first.org/data/v1/epss?cve=CVE-2026-21860
epss 0.00022 https://api.first.org/data/v1/epss?cve=CVE-2026-21860
epss 0.00022 https://api.first.org/data/v1/epss?cve=CVE-2026-21860
epss 0.00022 https://api.first.org/data/v1/epss?cve=CVE-2026-21860
epss 0.00022 https://api.first.org/data/v1/epss?cve=CVE-2026-21860
epss 0.00022 https://api.first.org/data/v1/epss?cve=CVE-2026-21860
epss 0.00022 https://api.first.org/data/v1/epss?cve=CVE-2026-21860
cvssv3.1 5.3 https://ftp.suse.com/pub/projects/security/yaml/suse-cvss-scores.yaml
cvssv3.1_qr MODERATE https://github.com/advisories/GHSA-87hc-h4r5-73f7
cvssv3.1 5.3 https://github.com/pallets/werkzeug
cvssv4 6.3 https://github.com/pallets/werkzeug
generic_textual MODERATE https://github.com/pallets/werkzeug
cvssv3.1 5.3 https://github.com/pallets/werkzeug/commit/7ae1d254e04a0c33e241ac1cca4783ce6c875ca3
cvssv4 6.3 https://github.com/pallets/werkzeug/commit/7ae1d254e04a0c33e241ac1cca4783ce6c875ca3
generic_textual MODERATE https://github.com/pallets/werkzeug/commit/7ae1d254e04a0c33e241ac1cca4783ce6c875ca3
ssvc Track https://github.com/pallets/werkzeug/commit/7ae1d254e04a0c33e241ac1cca4783ce6c875ca3
cvssv3.1 5.3 https://github.com/pallets/werkzeug/security/advisories/GHSA-87hc-h4r5-73f7
cvssv3.1_qr MODERATE https://github.com/pallets/werkzeug/security/advisories/GHSA-87hc-h4r5-73f7
cvssv4 6.3 https://github.com/pallets/werkzeug/security/advisories/GHSA-87hc-h4r5-73f7
generic_textual MODERATE https://github.com/pallets/werkzeug/security/advisories/GHSA-87hc-h4r5-73f7
ssvc Track https://github.com/pallets/werkzeug/security/advisories/GHSA-87hc-h4r5-73f7
cvssv3.1 5.3 https://nvd.nist.gov/vuln/detail/CVE-2026-21860
cvssv4 6.3 https://nvd.nist.gov/vuln/detail/CVE-2026-21860
generic_textual MODERATE https://nvd.nist.gov/vuln/detail/CVE-2026-21860
Reference id Reference type URL
https://api.first.org/data/v1/epss?cve=CVE-2026-21860
https://ftp.suse.com/pub/projects/security/yaml/suse-cvss-scores.yaml
https://github.com/pallets/werkzeug
https://github.com/pallets/werkzeug/commit/7ae1d254e04a0c33e241ac1cca4783ce6c875ca3
https://github.com/pallets/werkzeug/security/advisories/GHSA-87hc-h4r5-73f7
https://nvd.nist.gov/vuln/detail/CVE-2026-21860
GHSA-87hc-h4r5-73f7 https://github.com/advisories/GHSA-87hc-h4r5-73f7
No exploits are available.
Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L Found at https://ftp.suse.com/pub/projects/security/yaml/suse-cvss-scores.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

low

none
Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L Found at https://github.com/pallets/werkzeug
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:P/PR:N/UI:N/VC:N/VI:N/VA:L/SC:N/SI:N/SA:N Found at https://github.com/pallets/werkzeug
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

high

low

none
Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L Found at https://github.com/pallets/werkzeug/commit/7ae1d254e04a0c33e241ac1cca4783ce6c875ca3
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:P/PR:N/UI:N/VC:N/VI:N/VA:L/SC:N/SI:N/SA:N Found at https://github.com/pallets/werkzeug/commit/7ae1d254e04a0c33e241ac1cca4783ce6c875ca3
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

high

low

none
Vector: SSVCv2/E:N/A:N/T:P/P:M/B:A/M:M/D:T/2026-01-08T18:50:24Z/ Found at https://github.com/pallets/werkzeug/commit/7ae1d254e04a0c33e241ac1cca4783ce6c875ca3
Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L Found at https://github.com/pallets/werkzeug/security/advisories/GHSA-87hc-h4r5-73f7
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:P/PR:N/UI:N/VC:N/VI:N/VA:L/SC:N/SI:N/SA:N Found at https://github.com/pallets/werkzeug/security/advisories/GHSA-87hc-h4r5-73f7
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

high

low

none
Vector: SSVCv2/E:N/A:N/T:P/P:M/B:A/M:M/D:T/2026-01-08T18:50:24Z/ Found at https://github.com/pallets/werkzeug/security/advisories/GHSA-87hc-h4r5-73f7
Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L Found at https://nvd.nist.gov/vuln/detail/CVE-2026-21860
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:P/PR:N/UI:N/VC:N/VI:N/VA:L/SC:N/SI:N/SA:N Found at https://nvd.nist.gov/vuln/detail/CVE-2026-21860
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

high

low

none
Exploit Prediction Scoring System (EPSS)
Percentile 0.05881
EPSS Score 0.00022
Published At April 2, 2026, 12:55 p.m.
Date Actor Action Source VulnerableCode Version
2026-04-01T12:52:23.855340+00:00 GithubOSV Importer Import https://github.com/github/advisory-database/blob/main/advisories/github-reviewed/2026/01/GHSA-87hc-h4r5-73f7/GHSA-87hc-h4r5-73f7.json 38.0.0