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Vulnerability details: VCID-9m6a-v8jm-d3da
Vulnerability ID VCID-9m6a-v8jm-d3da
Aliases CVE-2021-39156
GHSA-hqxw-mm44-gc4r
Summary Istio Fragments in Path May Lead to Authorization Policy Bypass ### Impact Istio 1.11.0, 1.10.3 and below, and 1.9.7 and below contain a remotely exploitable vulnerability where an HTTP request with `#fragment` in the path may bypass Istio’s URI path based authorization policies. ### Patches * Istio 1.11.1 and above * Istio 1.10.4 and above * Istio 1.9.8 and above ### Workarounds A Lua filter may be written to normalize the path. This is similar to the Path normalization presented in the [Security Best Practices](https://istio.io/latest/docs/ops/best-practices/security/#case-normalization) guide. ### References More details can be found in the [Istio Security Bulletin](https://istio.io/latest/news/security/istio-security-2021-008) ### For more information If you have any questions or comments about this advisory, please email us at istio-security-vulnerability-reports@googlegroups.com
Status Published
Exploitability 0.5
Weighted Severity 8.0
Risk 4.0
Affected and Fixed Packages Package Details
Weaknesses (2)
CWE-706 Use of Incorrectly-Resolved Name or Reference
CWE-863 Incorrect Authorization
System Score Found at
cvssv3 8.3 https://access.redhat.com/hydra/rest/securitydata/cve/CVE-2021-39156.json
epss 0.00191 https://api.first.org/data/v1/epss?cve=CVE-2021-39156
epss 0.00191 https://api.first.org/data/v1/epss?cve=CVE-2021-39156
epss 0.00191 https://api.first.org/data/v1/epss?cve=CVE-2021-39156
epss 0.00191 https://api.first.org/data/v1/epss?cve=CVE-2021-39156
epss 0.00191 https://api.first.org/data/v1/epss?cve=CVE-2021-39156
epss 0.00191 https://api.first.org/data/v1/epss?cve=CVE-2021-39156
epss 0.00191 https://api.first.org/data/v1/epss?cve=CVE-2021-39156
epss 0.00191 https://api.first.org/data/v1/epss?cve=CVE-2021-39156
epss 0.00191 https://api.first.org/data/v1/epss?cve=CVE-2021-39156
epss 0.00191 https://api.first.org/data/v1/epss?cve=CVE-2021-39156
epss 0.00191 https://api.first.org/data/v1/epss?cve=CVE-2021-39156
epss 0.00191 https://api.first.org/data/v1/epss?cve=CVE-2021-39156
epss 0.00191 https://api.first.org/data/v1/epss?cve=CVE-2021-39156
epss 0.00191 https://api.first.org/data/v1/epss?cve=CVE-2021-39156
epss 0.00191 https://api.first.org/data/v1/epss?cve=CVE-2021-39156
epss 0.00191 https://api.first.org/data/v1/epss?cve=CVE-2021-39156
epss 0.00191 https://api.first.org/data/v1/epss?cve=CVE-2021-39156
epss 0.00191 https://api.first.org/data/v1/epss?cve=CVE-2021-39156
epss 0.00291 https://api.first.org/data/v1/epss?cve=CVE-2021-39156
epss 0.00291 https://api.first.org/data/v1/epss?cve=CVE-2021-39156
epss 0.00291 https://api.first.org/data/v1/epss?cve=CVE-2021-39156
epss 0.00291 https://api.first.org/data/v1/epss?cve=CVE-2021-39156
epss 0.00291 https://api.first.org/data/v1/epss?cve=CVE-2021-39156
epss 0.00291 https://api.first.org/data/v1/epss?cve=CVE-2021-39156
epss 0.00291 https://api.first.org/data/v1/epss?cve=CVE-2021-39156
epss 0.00291 https://api.first.org/data/v1/epss?cve=CVE-2021-39156
epss 0.00291 https://api.first.org/data/v1/epss?cve=CVE-2021-39156
epss 0.00291 https://api.first.org/data/v1/epss?cve=CVE-2021-39156
epss 0.00291 https://api.first.org/data/v1/epss?cve=CVE-2021-39156
cvssv3.1 8.1 https://github.com/istio/istio
generic_textual HIGH https://github.com/istio/istio
cvssv3.1 8.1 https://github.com/istio/istio/security/advisories/GHSA-hqxw-mm44-gc4r
generic_textual HIGH https://github.com/istio/istio/security/advisories/GHSA-hqxw-mm44-gc4r
cvssv3.1 8.1 https://istio.io/latest/news/security/istio-security-2021-008
generic_textual HIGH https://istio.io/latest/news/security/istio-security-2021-008
cvssv2 5.0 https://nvd.nist.gov/vuln/detail/CVE-2021-39156
cvssv3.1 7.5 https://nvd.nist.gov/vuln/detail/CVE-2021-39156
cvssv3.1 8.1 https://nvd.nist.gov/vuln/detail/CVE-2021-39156
generic_textual HIGH https://nvd.nist.gov/vuln/detail/CVE-2021-39156
archlinux High https://security.archlinux.org/AVG-2321
Reference id Reference type URL
https://access.redhat.com/hydra/rest/securitydata/cve/CVE-2021-39156.json
https://api.first.org/data/v1/epss?cve=CVE-2021-39156
https://github.com/istio/istio
https://github.com/istio/istio/security/advisories/GHSA-hqxw-mm44-gc4r
https://istio.io/latest/news/security/istio-security-2021-008
https://nvd.nist.gov/vuln/detail/CVE-2021-39156
1996915 https://bugzilla.redhat.com/show_bug.cgi?id=1996915
AVG-2321 https://security.archlinux.org/AVG-2321
cpe:2.3:a:istio:istio:*:*:*:*:*:*:*:* https://nvd.nist.gov/vuln/search/results?adv_search=true&isCpeNameSearch=true&query=cpe:2.3:a:istio:istio:*:*:*:*:*:*:*:*
RHSA-2021:3272 https://access.redhat.com/errata/RHSA-2021:3272
RHSA-2021:3273 https://access.redhat.com/errata/RHSA-2021:3273
No exploits are available.
Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:L/I:L/A:L Found at https://access.redhat.com/hydra/rest/securitydata/cve/CVE-2021-39156.json
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:R/S:U/C:H/I:H/A:N Found at https://github.com/istio/istio
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:R/S:U/C:H/I:H/A:N Found at https://github.com/istio/istio/security/advisories/GHSA-hqxw-mm44-gc4r
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:R/S:U/C:H/I:H/A:N Found at https://istio.io/latest/news/security/istio-security-2021-008
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: AV:N/AC:L/Au:N/C:P/I:N/A:N Found at https://nvd.nist.gov/vuln/detail/CVE-2021-39156
Exploitability (E) Access Vector (AV) Access Complexity (AC) Authentication (Au) Confidentiality Impact (C) Integrity Impact (I) Availability Impact (A)

high

functional

unproven

proof_of_concept

not_defined

local

adjacent_network

network

high

medium

low

multiple

single

none

none

partial

complete

none

partial

complete

none

partial

complete
Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N Found at https://nvd.nist.gov/vuln/detail/CVE-2021-39156
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:R/S:U/C:H/I:H/A:N Found at https://nvd.nist.gov/vuln/detail/CVE-2021-39156
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
Exploit Prediction Scoring System (EPSS)
Percentile 0.41398
EPSS Score 0.00191
Published At July 30, 2025, 12:55 p.m.
Date Actor Action Source VulnerableCode Version
2025-07-31T08:50:54.486201+00:00 GithubOSV Importer Import https://github.com/github/advisory-database/blob/main/advisories/github-reviewed/2021/08/GHSA-hqxw-mm44-gc4r/GHSA-hqxw-mm44-gc4r.json 37.0.0