CVE-2021-30823Network attack vector

HSTS bypass via insecure redirect handling

Published Oct 28, 2021 · Updated Aug 3, 2024

HSTS bypass in Apple WebKit products before their fixed releases allows man-in-the-middle attackers to bypass HTTPS upgrades via injected redirects. Safari followed an injected HTTP 302 redirect to an HSTS-protected host without upgrading to HTTPS, allowing non-Secure cookies to leak over intercepted traffic. Exploitation requires a privileged network position and affects confidentiality of cookies and requests, with no demonstrated integrity or availability impact.

CVSS severity6.5
Medium
EPSS probability2.23%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

HSTS bypass in Apple WebKit products before their fixed releases allows man-in-the-middle attackers to bypass HTTPS upgrades via injected redirects. Safari followed an injected HTTP 302 redirect to an HSTS-protected host without upgrading to HTTPS, allowing non-Secure cookies to leak over intercepted traffic. Exploitation requires a privileged network position and affects confidentiality of cookies and requests, with no demonstrated integrity or availability impact.

The record

CVE
CVE-2021-30823
Published
Oct 28, 2021
Updated
Aug 3, 2024
Vendor
Apple
Product
iOS and iPadOS
Classifications
T1557
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Oct 28, 2021CVE publishedPublication date reported by the CVE source.
  2. Aug 3, 2024Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=unspecified <14.8

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Apple · iOS and iPadOSversion=unspecified <14.8
Apple · Safariversion=unspecified <15
Apple · tvOSversion=unspecified <15
Apple · macOSversion=unspecified <12.0
Apple · watchOSversion=unspecified <8

Published CVSS scores

6.5NVDCVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:H/A:N
4.0NVDAV:N/AC:L/Au:S/C:N/I:P/A:N

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

T1557Adversary-in-the-Middle

Public exploit references

No public exploit references are available in this record.

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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