CVE-2021-21571Network attack vector

Preboot payload tampering via wildcard certificate acceptance

Published Jun 24, 2021 · Updated Sep 16, 2024

Improper certificate validation in Dell UEFI BIOS HTTPS Stack Gen 10 and Gen 11 allows remote attackers to tamper with preboot payloads. BIOSConnect accepts any valid wildcard certificate chained to a built-in CA instead of binding the certificate to Dell's download host. No product credentials are required, but exploitation requires network compromise, a trusted certificate, and physical initiation of BIOSConnect or HTTPS Boot, enabling payload tampering or an unspecified service interruption.

CVSS severity5.9
Medium
EPSS probability0.54%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Improper certificate validation in Dell UEFI BIOS HTTPS Stack Gen 10 and Gen 11 allows remote attackers to tamper with preboot payloads. BIOSConnect accepts any valid wildcard certificate chained to a built-in CA instead of binding the certificate to Dell's download host. No product credentials are required, but exploitation requires network compromise, a trusted certificate, and physical initiation of BIOSConnect or HTTPS Boot, enabling payload tampering or an unspecified service interruption.

The record

CVE
CVE-2021-21571
Published
Jun 24, 2021
Updated
Sep 16, 2024
Vendor
Dell
Product
Dell UEFI BIOS HTTPS Stack
Classifications
CWE-295, T1557
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Jun 24, 2021CVE publishedPublication date reported by the CVE source.
  2. Sep 16, 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=Gen 11, Gen 10

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Dell · Dell UEFI BIOS HTTPS Stackversion=Gen 11, Gen 10

Published CVSS scores

6.5NIST NVDCVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:L/A:H
5.8NIST NVDAV:N/AC:M/Au:N/C:N/I:P/A:P
5.9DellCVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:U/C:N/I:L/A:H

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

CWE-295Improper Certificate Validation
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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