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CVE

CVE-2023-28857

Apereo CAS is an open source multilingual single sign-on solution for the web. Apereo CAS can be configured to use authe

Apereo CAS is an open source multilingual single sign-on solution for the web. Apereo CAS can be configured to use authentication based on client X509 certificates. These certificates can be provided via TLS handshake or a special HTTP header, such as “ssl_client_cert”.

When checking the validity of the provided client certificate, X509CredentialsAuthenticationHandler performs check that this certificate is not revoked. To do so, it fetches URLs provided in the “CRL Distribution Points” extension of the certificate, which are taken from the certificate itself and therefore can be controlled by a malicious user. If the CAS server is configured to use an LDAP server for x509 authentication with a password, for example by setting a “cas.authn.x509.ldap.ldap-url” and “cas.authn.x509.ldap.bind-credential” properties, X509CredentialsAuthenticationHandler fetches revocation URLs from the certificate, which can be LDAP urls.

When making requests to this LDAP urls, Apereo CAS uses the same password as for initially configured LDAP server, which can lead to a password leak. An unauthenticated user can leak the password used to LDAP connection configured on server. This issue has been addressed in version 6.6.6.

Users are advised to upgrade. There are no known workarounds for this vulnerability.

MEDIUM · CVSS 4 EPSS 0.0027
Monitor
  • No active-exploitation, high-EPSS, or public-exploit signals - routine patching cadence
Sigma rules0 YARA rules0
Look this up elsewhere - one-click external pivots
NVDCVE.orgCISAVulnersExploit-DBGitHub PoCVulnCheck KEVGreyNoise
▸ How to read a CVE - triage first, then detect and patch
This page is every public fact about CVE-2023-28857, cross-linked. Its job is to answer one question fast - does this need my attention now? - and then hand you the two things you do about it. Here is how an analyst reads it.
Triage: should I act now? Four signals, and they are not interchangeable:
CVSSseverity - how bad it is IF exploited, 0-10. A high CVSS alone is not urgency; a flaw can be a perfect 10 and never actually be attacked. EPSSprobability - a model’s estimate of the chance it is exploited in the next 30 days, 0-1. This is the “will it actually happen” signal. CISA KEVconfirmed - it is being exploited in the wild right now. The strongest signal on the page; KEV beats any score. Weaponisedavailability - public exploits / PoCs, and especially Metasploit modules rated Excellent / Great. Reliable, packaged exploit code means low-skill attackers can use it today.
How they combine: KEV, or a dependable Metasploit module, means patch now regardless of CVSS. High CVSS + low EPSS + no exploit is real but not an emergency - schedule it. Low CVSS but KEV-listed still gets patched now. The verdict above already weighed these for you; this is how it got there.
Then what - two workflows:
Detectwhen you cannot patch today, follow this CVE to the ATT&CK techniques it enables, then Build a SIEM detection (the green button) - author a rule, test it in Atomic, deploy it. That buys visibility while the patch waits. PatchAffected products / packages tell you if you are exposed; Fixed versions by distribution and Vendor advisories give the exact version that closes it.
Reading order for the panels below: verdict + badges, then Public exploits / Metasploit (is it weaponised), then ATT&CK techniques + Sigma / IDS rules (can I detect it), then Affected products / packages + Fixed versions (am I exposed, what patches it), then Threat actors / IOCs (who uses it), then Scoring & timeline / references (the evidence).
◆

ATT&CK techniques

20

Techniques this CVE enables - linked via CWECAPECATT&CK. High◆ = named directly in ATT&CK or Nuclei templates.

T1007 · System Service Discovery T1016 · System Network Configuration Discovery T1018 · Remote System Discovery T1021 · Remote Services T1021.002 · SMB/Windows Admin Shares T1033 · System Owner/User Discovery T1036.005 · Match Legitimate Resource Name or Location T1046 · Network Service Discovery T1049 · System Network Connections Discovery T1057 · Process Discovery T1069 · Permission Groups Discovery T1078 · Valid Accounts T1082 · System Information Discovery T1083 · File and Directory Discovery T1087 · Account Discovery T1110.004 · Credential Stuffing T1111 · Multi-Factor Authentication Interception T1114.002 · Remote Email Collection T1120 · Peripheral Device Discovery T1124 · System Time Discovery
▤ Build a SIEM detection for these techniques
▤

CAPEC attack patterns

12

Attack patterns this CVE enables - the bridge from weakness to ATT&CK technique.

CAPEC-CAPEC-102 · Session Sidejacking CAPEC-CAPEC-116 · Excavation CAPEC-CAPEC-13 · Subverting Environment Variable Values CAPEC-CAPEC-169 · Footprinting CAPEC-CAPEC-22 · Exploiting Trust in Client CAPEC-CAPEC-224 · Fingerprinting CAPEC-CAPEC-285 · ICMP Echo Request Ping CAPEC-CAPEC-287 · TCP SYN Scan CAPEC-CAPEC-290 · Enumerate Mail Exchange (MX) Records CAPEC-CAPEC-291 · DNS Zone Transfers CAPEC-CAPEC-292 · Host Discovery CAPEC-CAPEC-293 · Traceroute Route Enumeration
⬡

Weakness Classification

CWE-200Exposure of Sensitive Information to an Unauthorized Actor
CWE-522Insufficiently Protected Credentials
▤

Affected Products & Versions

2
apereo central authentication service>= 6.5.0 and < 6.5.9.1
apereo central authentication service>= 6.6.0 and < 6.6.6
▤

Affected Packages

1
Language-ecosystem packages (from OSV) tied to this CVE, with the version that fixes it - the dependency-level detail NVD doesn’t carry.
Maven org.apereo.cas:cas-server-support-x509-core MODERATE fixed in 6.6.6
▣

Scoring & Timeline

4
MEDIUM · CVSS v3.1 · [email protected]
View on NVD
Attack Vector
Network Adjacent Local Physical
Attack Complexity
Low High
Privileges Required
None Low High
User Interaction
None Required
Scope
Unchanged Changed
Confidentiality
None Low High
Integrity
None Low High
Availability
None Low High
Published to NVD27 Jun 2023 · 06:15 PM
CVSS VectorCVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:C/C:L/I:N/A:N
SSVC triage · cisa-vulnrichment
Exploitation
poc
Automatable
no
Technical impact
partial
SSVC asks the questions that actually drive patch urgency: is it being exploited, can attacks be automated, and how total is the impact.
🔗

References & Sources

3
Source URLs (vendor pages, mailing lists, write-ups). Exploit/PoC links are in their own section above to avoid duplication.
https://apereo.github.io/2023/02/20/x509-vuln/Third Party Advisory
https://github.com/apereo/cas/releases/tag/v6.6.6Release Notes
https://securitylab.github.com/advisories/GHSL-2023-009_Apereo_CAS/Third Party Advisory
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