CVE-2021-28091Network attack vector

Authentication bypass via partially verified SAML assertions

Published Jun 4, 2021 · Updated Aug 3, 2024

XML signature wrapping in Entr'ouvert Lasso before 2.7.0 allows remote attackers to impersonate users through crafted SAML responses. Lasso verifies only the first assertion's signature but returns the last assertion, so an appended unsigned assertion controls the identity. Exploitation requires a valid SAML response obtained as a recognized identity-provider user or through interception, and permits impersonation or access-control bypass.

CVSS severity7.5
High
EPSS probability1.32%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

XML signature wrapping in Entr'ouvert Lasso before 2.7.0 allows remote attackers to impersonate users through crafted SAML responses. Lasso verifies only the first assertion's signature but returns the last assertion, so an appended unsigned assertion controls the identity. Exploitation requires a valid SAML response obtained as a recognized identity-provider user or through interception, and permits impersonation or access-control bypass.

The record

CVE
CVE-2021-28091
Published
Jun 4, 2021
Updated
Aug 3, 2024
Vendor
Unknown vendor
Product
Unknown product
Classifications
CWE-347, T1078
Attack vector
network
Privileges
Unavailable

Timeline

How it unfolded

  1. Jun 4, 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?

Affected buildAffected product and version details are unavailable.

What conditions does exploitation require?

Attack vectornetwork
Required privilegesUnavailable in this record.

What is affected?

Affected products and versions are unavailable in this record.

Published CVSS scores

7.5NIST NVDCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N
5.0NIST NVDAV:N/AC:L/Au:N/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.

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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
PrivilegesUnavailable
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-347Improper Verification of Cryptographic Signature
T1078Valid Accounts

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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