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Fencer Intel
high 7.5

CVE-2021-27516 json

URIjs Hostname spoofing via backslashes in URL

published 5y ago modified 4mo ago also GHSA-p6j9-7xhc-rhwp , EUVD-2021-0686

cvss
7.5
version 3.1, NVD
cisa kev
Not listed
not in CISA's catalog
epss
2.5%
EPSS 2.5% chance of exploitation in 30 days, percentile 84%
public exploits
0
none known

Summary

URI.js (aka urijs) before 1.19.6 mishandles certain uses of backslash such as http:\/ and interprets the URI as a relative path.

Patch / fix

  • npm urijs 1.19.6
  • uri.js_project uri.js 1.19.6

Is CVE-2021-27516 in your dependencies? Fencer shows which of your repositories are affected as soon as an advisory lands, and opens the fix as a pull request.

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Vendor advisories

What the vendors themselves say about their products: affected, fixed or not affected, and what to do.

red hat product security vex CVE-2021-27516 updated cvss 7.5

nodejs-urijs: mishandling certain uses of backslash may lead to confidentiality compromise

  • Red Hat Quay v3 quay/quay-rhel8 v3.6.0-62
    fixed: vendor fix RHSA-2021:3917
  • Red Hat Quay v3 quay/clair-rhel8 v3.6.0-70, quay/quay-builder-rhel8 v3.6.0-44, quay/quay-operator-rhel8 v3.6.0-43, quay/quay-operator-bundle v3.6.0-48, quay/quay-bridge-operator-rhel8 v3.6.0-40, quay/quay-bridge-operator-bundle v3.6.0-35, +3 more Red Hat Advanced Cluster Management for Kubernetes 2 rhacm2/mcm-topology-rhel8, rhacm2/application-ui-rhel8
    not affected: vulnerable code not present

Red Hat CSAF VEX © Red Hat, Inc., from https://security.access.redhat.com/data/csaf/v2/vex/; changed: reduced to product statuses and remediations. CC BY 4.0 · csaf

Exploit prediction

2.48% chance of exploitation in the next 30 days, higher than 84% of all scored CVEs (FIRST EPSS, 2026-11-09).

Exploits and checks

  • advisory.checkmarx.net https://advisory.checkmarx.net/advisory/CX-2021-4305 referenced PoC, tagged "exploit" by a source, unverified

CVSS scores

assigned by version score vector
NVD 3.1 7.5 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N
NVD 2.0 5.0 AV:N/AC:L/Au:N/C:P/I:N/A:N
GitHub 3.1 7.5 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N

Affected packages

ecosystem package affected fixed in
npm urijs
<1.19.6
1.19.6

Classification

Weakness
  • CWE-20 Improper Input Validation

References

Sources

Fencer Intel keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.