CVE-2021-3618Public exploitNetwork attack vector

Cookie theft and XSS via TLS confusion

Published Mar 23, 2022 · Updated Aug 3, 2024

ALPACA protocol confusion allows man-in-the-middle attackers to steal cookies or execute JavaScript through redirected TLS traffic. TLS authenticates certificate identity but not the destination address, port, or application protocol, so a redirected peer with a compatible certificate completes a valid session. Exploitation requires compatible certificates across different-protocol services and traffic redirection at the TCP/IP layer; demonstrated outcomes include cookie theft and same-origin JavaScript execution.

CVSS severity7.4
High
EPSS probability2.04%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

ALPACA protocol confusion allows man-in-the-middle attackers to steal cookies or execute JavaScript through redirected TLS traffic. TLS authenticates certificate identity but not the destination address, port, or application protocol, so a redirected peer with a compatible certificate completes a valid session. Exploitation requires compatible certificates across different-protocol services and traffic redirection at the TCP/IP layer; demonstrated outcomes include cookie theft and same-origin JavaScript execution.

The record

CVE
CVE-2021-3618
Published
Mar 23, 2022
Updated
Aug 3, 2024
Vendor
Unknown vendor
Product
Unknown product
Classifications
CWE-295, T1539
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Mar 23, 2022CVE 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?

Affected buildAffected product and version details are unavailable.

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Affected products and versions are unavailable in this record.

Published CVSS scores

7.4NIST NVDCVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/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 9, 2026Sep 15, 2026
Latest reporting daySep 15, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitPublished

Weakness, pattern, technique

CWE-295Improper Certificate Validation
T1539Steal Web Session Cookie

Public exploit references

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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