CWE-295
AllowedImproper Certificate Validation
Abstraction: Base · Status: Draft
The product does not validate, or incorrectly validates, a certificate.
1919 vulnerabilities reference this CWE, most recent first.
GHSA-7XRH-HQFC-G7QR
Vulnerability from github – Published: 2026-03-07 09:30 – Updated: 2026-03-10 19:32Hostname verification in Apache ZooKeeper ZKTrustManager falls back to reverse DNS (PTR) when IP SAN validation fails, allowing attackers who control or spoof PTR records to impersonate ZooKeeper servers or clients with a valid certificate for the PTR name. It's important to note that attacker must present a certificate which is trusted by ZKTrustManager which makes the attack vector harder to exploit. Users are recommended to upgrade to version 3.8.6 or 3.9.5, which fixes this issue by introducing a new configuration option to disable reverse DNS lookup in client and quorum protocols.
{
"affected": [
{
"package": {
"ecosystem": "Maven",
"name": "org.apache.zookeeper:zookeeper"
},
"ranges": [
{
"events": [
{
"introduced": "3.8.0"
},
{
"fixed": "3.8.6"
}
],
"type": "ECOSYSTEM"
}
]
},
{
"package": {
"ecosystem": "Maven",
"name": "org.apache.zookeeper:zookeeper"
},
"ranges": [
{
"events": [
{
"introduced": "3.9.0"
},
{
"fixed": "3.9.5"
}
],
"type": "ECOSYSTEM"
}
]
}
],
"aliases": [
"CVE-2026-24281"
],
"database_specific": {
"cwe_ids": [
"CWE-295",
"CWE-297"
],
"github_reviewed": true,
"github_reviewed_at": "2026-03-10T19:32:52Z",
"nvd_published_at": "2026-03-07T09:16:07Z",
"severity": "HIGH"
},
"details": "Hostname verification in Apache ZooKeeper ZKTrustManager falls back to reverse DNS (PTR) when IP SAN validation fails, allowing attackers who control or spoof PTR records to impersonate ZooKeeper servers or clients with a valid certificate for the PTR name. It\u0027s important to note that attacker must present a certificate which is trusted by ZKTrustManager which makes the attack vector harder to exploit. Users are recommended to upgrade to version 3.8.6 or 3.9.5, which fixes this issue by introducing a new configuration option to disable reverse DNS lookup in client and quorum protocols.",
"id": "GHSA-7xrh-hqfc-g7qr",
"modified": "2026-03-10T19:32:52Z",
"published": "2026-03-07T09:30:15Z",
"references": [
{
"type": "ADVISORY",
"url": "https://nvd.nist.gov/vuln/detail/CVE-2026-24281"
},
{
"type": "WEB",
"url": "https://github.com/apache/zookeeper/commit/66c4efecdda1302d9cfb3af9eedb122b74452bf3"
},
{
"type": "PACKAGE",
"url": "https://github.com/apache/zookeeper"
},
{
"type": "WEB",
"url": "https://issues.apache.org/jira/browse/ZOOKEEPER-4986"
},
{
"type": "WEB",
"url": "https://lists.apache.org/thread/088ddsbrzhd5lxzbqf5n24yg0mwh9jt2"
},
{
"type": "WEB",
"url": "http://www.openwall.com/lists/oss-security/2026/03/07/4"
}
],
"schema_version": "1.4.0",
"severity": [
{
"score": "CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:N",
"type": "CVSS_V3"
}
],
"summary": "Apache ZooKeeper: Reverse-DNS fallback enables hostname verification bypass in ZooKeeper ZKTrustManager"
}
GHSA-825C-4W2M-H7FV
Vulnerability from github – Published: 2024-03-07 18:30 – Updated: 2025-02-13 18:32Under certain configurations of --tlsCAFile and tls.CAFile, MongoDB Server may skip peer certificate validation which may result in untrusted connections to succeed. This may effectively reduce the security guarantees provided by TLS and open connections that should have been closed due to failing certificate validation. This issue affects MongoDB Server v7.0 versions prior to and including 7.0.5, MongoDB Server v6.0 versions prior to and including 6.0.13, MongoDB Server v5.0 versions prior to and including 5.0.24 and MongoDB Server v4.4 versions prior to and including 4.4.28.
Required Configuration : A server process will allow incoming connections to skip peer certificate validation if the server process was started with TLS enabled (net.tls.mode set to allowTLS, preferTLS, or requireTLS) and without a net.tls.CAFile configured.
{
"affected": [],
"aliases": [
"CVE-2024-1351"
],
"database_specific": {
"cwe_ids": [
"CWE-295"
],
"github_reviewed": false,
"github_reviewed_at": null,
"nvd_published_at": "2024-03-07T17:15:12Z",
"severity": "HIGH"
},
"details": "Under certain configurations of --tlsCAFile and tls.CAFile, MongoDB Server may skip peer certificate validation which may result in untrusted connections to succeed. This may effectively reduce the security guarantees provided by TLS and open connections that should have been closed due to failing certificate validation. This issue affects MongoDB Server v7.0 versions prior to and including 7.0.5, MongoDB Server v6.0 versions prior to and including 6.0.13, MongoDB Server v5.0 versions prior to and including 5.0.24 and MongoDB Server v4.4 versions prior to and including 4.4.28.\n\nRequired Configuration : A server process will allow incoming connections to skip peer certificate validation if the server process was started with TLS enabled (net.tls.mode set to allowTLS, preferTLS, or requireTLS) and without a net.tls.CAFile configured.",
"id": "GHSA-825c-4w2m-h7fv",
"modified": "2025-02-13T18:32:20Z",
"published": "2024-03-07T18:30:28Z",
"references": [
{
"type": "ADVISORY",
"url": "https://nvd.nist.gov/vuln/detail/CVE-2024-1351"
},
{
"type": "WEB",
"url": "https://jira.mongodb.org/browse/SERVER-72839"
},
{
"type": "WEB",
"url": "https://security.netapp.com/advisory/ntap-20240524-0010"
},
{
"type": "WEB",
"url": "https://www.mongodb.com/docs/manual/release-notes/4.4/#4.4.29---february-28--2024"
},
{
"type": "WEB",
"url": "https://www.mongodb.com/docs/manual/release-notes/7.0/#7.0.6---feb-28--2024"
},
{
"type": "WEB",
"url": "https://www.mongodb.com/docs/v5.0/release-notes/5.0/#5.0.25---february-28--2024"
},
{
"type": "WEB",
"url": "https://www.mongodb.com/docs/v6.0/release-notes/6.0/#6.0.14---feb-28--2024"
}
],
"schema_version": "1.4.0",
"severity": [
{
"score": "CVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H",
"type": "CVSS_V3"
}
]
}
GHSA-828C-XPC3-JQW5
Vulnerability from github – Published: 2022-05-17 02:48 – Updated: 2022-05-17 02:48DMM Movie Player App for Android before 1.2.1, and DMM Movie Player App for iPhone/iPad before 2.1.3 does not verify SSL certificates.
{
"affected": [],
"aliases": [
"CVE-2016-4829"
],
"database_specific": {
"cwe_ids": [
"CWE-295"
],
"github_reviewed": false,
"github_reviewed_at": null,
"nvd_published_at": "2017-04-21T14:59:00Z",
"severity": "MODERATE"
},
"details": "DMM Movie Player App for Android before 1.2.1, and DMM Movie Player App for iPhone/iPad before 2.1.3 does not verify SSL certificates.",
"id": "GHSA-828c-xpc3-jqw5",
"modified": "2022-05-17T02:48:18Z",
"published": "2022-05-17T02:48:18Z",
"references": [
{
"type": "ADVISORY",
"url": "https://nvd.nist.gov/vuln/detail/CVE-2016-4829"
},
{
"type": "WEB",
"url": "http://jvn.jp/en/jp/JVN39594409/index.html"
},
{
"type": "WEB",
"url": "http://jvndb.jvn.jp/en/contents/2016/JVNDB-2016-000120.html"
}
],
"schema_version": "1.4.0",
"severity": [
{
"score": "CVSS:3.0/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:H/A:N",
"type": "CVSS_V3"
}
]
}
GHSA-82FM-WPC2-5PMP
Vulnerability from github – Published: 2026-04-27 15:30 – Updated: 2026-05-05 22:05Improper Certificate Validation via Global SSL Context Downgrade in Apache Storm Prometheus Reporter
Versions Affected: from 2.6.3 to 2.8.6
Description:
In production deployments where an administrator enables storm.daemon.metrics.reporter.plugin.prometheus.skip_tls_validation (by default it is disabled) intending to affect only the Prometheus reporter, the undocumented global side effect creates an attack surface across every TLS-protected communication channel in the Storm daemon.
The PrometheusPreparableReporter class implements an INSECURE_TRUST_MANAGER that accepts all SSL certificates without validation, with empty checkClientTrusted and checkServerTrusted methods. Most critically, when the storm.daemon.metrics.reporter.plugin.prometheus.skip_tls_validation configuration option is enabled (default = disabled) for HTTPS Prometheus PushGateway connections, the INSECURE_CONNECTION_FACTORY calls SSLContext.setDefault(sslContext), which globally replaces the JVM's default SSL context rather than applying the insecure context only to the Prometheus connection. This payload flows through storm.yaml configuration → PrometheusPreparableReporter.prepare() → INSECURE_CONNECTION_FACTORY → SSLContext.setDefault(), resulting in a JVM-wide TLS security downgrade. All subsequent HTTPS connections in the process - including ZooKeeper, Thrift, Netty, and UI connections - silently trust all certificates, including self-signed, expired, and attacker-generated ones, enabling man-in-the-middle interception of cluster state, topology submissions, tuple data, and administrative credentials.
Mitigation: 2.x users should upgrade to 2.8.7 if the Prometheus Metrics Reporter is used. Prometheus Metrics Reporter Users who cannot upgrade immediately should remove the storm.daemon.metrics.reporter.plugin.prometheus.skip_tls_validation: true setting from their storm.yaml configuration and instead configure a proper truststore containing the PushGateway's certificate.
{
"affected": [
{
"package": {
"ecosystem": "Maven",
"name": "org.apache.storm:storm-metrics-prometheus"
},
"ranges": [
{
"events": [
{
"introduced": "2.6.3"
},
{
"fixed": "2.8.7"
}
],
"type": "ECOSYSTEM"
}
]
}
],
"aliases": [
"CVE-2026-40557"
],
"database_specific": {
"cwe_ids": [
"CWE-295"
],
"github_reviewed": true,
"github_reviewed_at": "2026-05-05T22:05:03Z",
"nvd_published_at": "2026-04-27T14:16:48Z",
"severity": "MODERATE"
},
"details": "Improper Certificate Validation via Global SSL Context Downgrade in Apache Storm Prometheus Reporter\n\n\nVersions Affected: from 2.6.3 to 2.8.6\n\n\nDescription:\u00a0\n\nIn production deployments where an administrator enables storm.daemon.metrics.reporter.plugin.prometheus.skip_tls_validation\u00a0(by default it is disabled)\u00a0intending to affect only the Prometheus reporter, the undocumented global side effect creates an attack surface across every TLS-protected communication channel in the Storm daemon.\n\n\nThe PrometheusPreparableReporter class implements an INSECURE_TRUST_MANAGER that accepts all SSL certificates without validation, with empty checkClientTrusted and checkServerTrusted methods. Most critically, when the storm.daemon.metrics.reporter.plugin.prometheus.skip_tls_validation configuration option is enabled (default = disabled) for HTTPS Prometheus PushGateway connections, the INSECURE_CONNECTION_FACTORY calls SSLContext.setDefault(sslContext), which globally replaces the JVM\u0027s default SSL context rather than applying the insecure context only to the Prometheus connection. This payload flows through storm.yaml configuration \u2192 PrometheusPreparableReporter.prepare() \u2192 INSECURE_CONNECTION_FACTORY \u2192 SSLContext.setDefault(), resulting in a JVM-wide TLS security downgrade. All subsequent HTTPS connections in the process - including ZooKeeper, Thrift, Netty, and UI connections - silently trust all certificates, including self-signed, expired, and attacker-generated ones, enabling man-in-the-middle interception of cluster state, topology submissions, tuple data, and administrative credentials.\n\n\n\n\nMitigation: 2.x users should upgrade to 2.8.7 if the Prometheus Metrics Reporter is used. Prometheus Metrics Reporter Users who cannot upgrade immediately should remove the storm.daemon.metrics.reporter.plugin.prometheus.skip_tls_validation: true setting from their storm.yaml configuration and instead configure a proper truststore containing the PushGateway\u0027s certificate.",
"id": "GHSA-82fm-wpc2-5pmp",
"modified": "2026-05-05T22:05:03Z",
"published": "2026-04-27T15:30:52Z",
"references": [
{
"type": "ADVISORY",
"url": "https://nvd.nist.gov/vuln/detail/CVE-2026-40557"
},
{
"type": "PACKAGE",
"url": "https://github.com/apache/storm"
},
{
"type": "WEB",
"url": "https://lists.apache.org/thread/f5bv68z1y5xstz22psjk05p3wn86knjq"
},
{
"type": "WEB",
"url": "http://www.openwall.com/lists/oss-security/2026/04/25/2"
}
],
"schema_version": "1.4.0",
"severity": [
{
"score": "CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:N",
"type": "CVSS_V3"
}
],
"summary": "Apache Storm Prometheus Reporter vulnerable to Improper Certificate Validation via Global SSL Context Downgrade"
}
GHSA-82JC-CV6X-R223
Vulnerability from github – Published: 2022-05-24 17:06 – Updated: 2025-10-22 00:31A spoofing vulnerability exists in the way Windows CryptoAPI (Crypt32.dll) validates Elliptic Curve Cryptography (ECC) certificates.An attacker could exploit the vulnerability by using a spoofed code-signing certificate to sign a malicious executable, making it appear the file was from a trusted, legitimate source, aka 'Windows CryptoAPI Spoofing Vulnerability'.
{
"affected": [],
"aliases": [
"CVE-2020-0601"
],
"database_specific": {
"cwe_ids": [
"CWE-295"
],
"github_reviewed": false,
"github_reviewed_at": null,
"nvd_published_at": "2020-01-14T23:15:00Z",
"severity": "MODERATE"
},
"details": "A spoofing vulnerability exists in the way Windows CryptoAPI (Crypt32.dll) validates Elliptic Curve Cryptography (ECC) certificates.An attacker could exploit the vulnerability by using a spoofed code-signing certificate to sign a malicious executable, making it appear the file was from a trusted, legitimate source, aka \u0027Windows CryptoAPI Spoofing Vulnerability\u0027.",
"id": "GHSA-82jc-cv6x-r223",
"modified": "2025-10-22T00:31:49Z",
"published": "2022-05-24T17:06:15Z",
"references": [
{
"type": "ADVISORY",
"url": "https://nvd.nist.gov/vuln/detail/CVE-2020-0601"
},
{
"type": "WEB",
"url": "https://portal.msrc.microsoft.com/en-US/security-guidance/advisory/CVE-2020-0601"
},
{
"type": "WEB",
"url": "https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2020-0601"
},
{
"type": "WEB",
"url": "http://packetstormsecurity.com/files/155960/CurveBall-Microsoft-Windows-CryptoAPI-Spoofing-Proof-Of-Concept.html"
},
{
"type": "WEB",
"url": "http://packetstormsecurity.com/files/155961/CurveBall-Microsoft-Windows-CryptoAPI-Spoofing-Proof-Of-Concept.html"
}
],
"schema_version": "1.4.0",
"severity": [
{
"score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:N",
"type": "CVSS_V3"
}
]
}
GHSA-8336-MXP6-V5H9
Vulnerability from github – Published: 2018-10-16 19:51 – Updated: 2021-06-11 15:34Failure to validate certificates in OPC Foundation UA Client Applications communicating without security allows attackers with control over a piece of network infrastructure to decrypt passwords.
{
"affected": [
{
"database_specific": {
"last_known_affected_version_range": "\u003c= 1.4.352.12"
},
"package": {
"ecosystem": "NuGet",
"name": "OPCFoundation.NetStandard.Opc.Ua"
},
"ranges": [
{
"events": [
{
"introduced": "0"
},
{
"fixed": "1.4.353.15"
}
],
"type": "ECOSYSTEM"
}
]
}
],
"aliases": [
"CVE-2018-12087"
],
"database_specific": {
"cwe_ids": [
"CWE-295"
],
"github_reviewed": true,
"github_reviewed_at": "2020-06-16T21:24:04Z",
"nvd_published_at": null,
"severity": "MODERATE"
},
"details": "Failure to validate certificates in OPC Foundation UA Client Applications communicating without security allows attackers with control over a piece of network infrastructure to decrypt passwords.",
"id": "GHSA-8336-mxp6-v5h9",
"modified": "2021-06-11T15:34:21Z",
"published": "2018-10-16T19:51:18Z",
"references": [
{
"type": "ADVISORY",
"url": "https://nvd.nist.gov/vuln/detail/CVE-2018-12087"
},
{
"type": "ADVISORY",
"url": "https://github.com/advisories/GHSA-8336-mxp6-v5h9"
},
{
"type": "WEB",
"url": "https://opcfoundation-onlineapplications.org/faq/SecurityBulletins/OPC_Foundation_Security_Bulletin_CVE-2018-12087.pdf"
}
],
"schema_version": "1.4.0",
"severity": [
{
"score": "CVSS:3.0/AV:P/AC:L/PR:N/UI:N/S:C/C:H/I:N/A:N",
"type": "CVSS_V3"
}
],
"summary": "Moderate severity vulnerability that affects OPCFoundation.NetStandard.Opc.Ua"
}
GHSA-8382-WRQG-HQW9
Vulnerability from github – Published: 2024-07-09 18:30 – Updated: 2024-07-09 18:30A vulnerability in Samsung Exynos Modem 5300 allows a Man-in-the-Middle (MITM) attacker to downgrade the security mode of packets going to the victim, enabling the attacker to send messages to the victim in plaintext.
{
"affected": [],
"aliases": [
"CVE-2024-28067"
],
"database_specific": {
"cwe_ids": [
"CWE-295"
],
"github_reviewed": false,
"github_reviewed_at": null,
"nvd_published_at": "2024-07-09T18:15:09Z",
"severity": "MODERATE"
},
"details": "A vulnerability in Samsung Exynos Modem 5300 allows a Man-in-the-Middle (MITM) attacker to downgrade the security mode of packets going to the victim, enabling the attacker to send messages to the victim in plaintext.",
"id": "GHSA-8382-wrqg-hqw9",
"modified": "2024-07-09T18:30:53Z",
"published": "2024-07-09T18:30:53Z",
"references": [
{
"type": "ADVISORY",
"url": "https://nvd.nist.gov/vuln/detail/CVE-2024-28067"
},
{
"type": "WEB",
"url": "https://semiconductor.samsung.com/support/quality-support/product-security-updates"
},
{
"type": "WEB",
"url": "https://semiconductor.samsung.com/support/quality-support/product-security-updates/cve-2024-28067"
}
],
"schema_version": "1.4.0",
"severity": [
{
"score": "CVSS:3.1/AV:A/AC:H/PR:N/UI:N/S:U/C:N/I:H/A:N",
"type": "CVSS_V3"
}
]
}
GHSA-83C4-8F8C-MF3P
Vulnerability from github – Published: 2026-02-05 21:32 – Updated: 2026-02-05 21:32Tanium addressed an improper certificate validation vulnerability in Tanium Appliance.
{
"affected": [],
"aliases": [
"CVE-2025-15323"
],
"database_specific": {
"cwe_ids": [
"CWE-295"
],
"github_reviewed": false,
"github_reviewed_at": null,
"nvd_published_at": "2026-02-05T19:15:52Z",
"severity": "LOW"
},
"details": "Tanium addressed an improper certificate validation vulnerability in Tanium Appliance.",
"id": "GHSA-83c4-8f8c-mf3p",
"modified": "2026-02-05T21:32:41Z",
"published": "2026-02-05T21:32:41Z",
"references": [
{
"type": "ADVISORY",
"url": "https://nvd.nist.gov/vuln/detail/CVE-2025-15323"
},
{
"type": "WEB",
"url": "https://security.tanium.com/TAN-2025-031"
}
],
"schema_version": "1.4.0",
"severity": [
{
"score": "CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:N/A:N",
"type": "CVSS_V3"
}
]
}
GHSA-844J-8V3Q-83RF
Vulnerability from github – Published: 2025-01-26 18:30 – Updated: 2025-01-26 18:30IBM Cognos Mobile Client 1.1 iOS may be vulnerable to information disclosure through man in the middle techniques due to the lack of certificate pinning.
{
"affected": [],
"aliases": [
"CVE-2023-38009"
],
"database_specific": {
"cwe_ids": [
"CWE-295"
],
"github_reviewed": false,
"github_reviewed_at": null,
"nvd_published_at": "2025-01-26T16:15:30Z",
"severity": "MODERATE"
},
"details": "IBM Cognos Mobile Client 1.1 iOS may be vulnerable to information disclosure through man in the middle techniques due to the lack of certificate pinning.",
"id": "GHSA-844j-8v3q-83rf",
"modified": "2025-01-26T18:30:32Z",
"published": "2025-01-26T18:30:32Z",
"references": [
{
"type": "ADVISORY",
"url": "https://nvd.nist.gov/vuln/detail/CVE-2023-38009"
},
{
"type": "WEB",
"url": "https://www.ibm.com/support/pages/node/7172691"
},
{
"type": "WEB",
"url": "https://www.ibm.com/support/pages/node/7172692"
}
],
"schema_version": "1.4.0",
"severity": [
{
"score": "CVSS:3.1/AV:P/AC:H/PR:N/UI:N/S:U/C:H/I:N/A:N",
"type": "CVSS_V3"
}
]
}
GHSA-849M-V43M-PPMQ
Vulnerability from github – Published: 2022-05-24 16:55 – Updated: 2023-02-16 03:30IMAPFilter through 2.6.12 does not validate the hostname in an SSL certificate.
{
"affected": [],
"aliases": [
"CVE-2016-10937"
],
"database_specific": {
"cwe_ids": [
"CWE-295"
],
"github_reviewed": false,
"github_reviewed_at": null,
"nvd_published_at": "2019-09-08T16:15:00Z",
"severity": "HIGH"
},
"details": "IMAPFilter through 2.6.12 does not validate the hostname in an SSL certificate.",
"id": "GHSA-849m-v43m-ppmq",
"modified": "2023-02-16T03:30:29Z",
"published": "2022-05-24T16:55:38Z",
"references": [
{
"type": "ADVISORY",
"url": "https://nvd.nist.gov/vuln/detail/CVE-2016-10937"
},
{
"type": "WEB",
"url": "https://github.com/lefcha/imapfilter/issues/142"
},
{
"type": "WEB",
"url": "https://bugs.debian.org/939702"
},
{
"type": "WEB",
"url": "https://lists.debian.org/debian-lts-announce/2019/10/msg00040.html"
},
{
"type": "WEB",
"url": "https://lists.fedoraproject.org/archives/list/package-announce@lists.fedoraproject.org/message/GBNDFMAIUA6PQMV2P6OKIP7JZQEWX7D2"
},
{
"type": "WEB",
"url": "https://lists.fedoraproject.org/archives/list/package-announce@lists.fedoraproject.org/message/IQUH2TOCNEST7JB2RJVVJT3RZS5XZCFZ"
},
{
"type": "WEB",
"url": "http://lists.opensuse.org/opensuse-security-announce/2020-05/msg00042.html"
},
{
"type": "WEB",
"url": "http://lists.opensuse.org/opensuse-security-announce/2020-06/msg00002.html"
}
],
"schema_version": "1.4.0",
"severity": [
{
"score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N",
"type": "CVSS_V3"
}
]
}
Mitigation
Certificates should be carefully managed and checked to assure that data are encrypted with the intended owner's public key.
Mitigation
If certificate pinning is being used, ensure that all relevant properties of the certificate are fully validated before the certificate is pinned, including the hostname.
CAPEC-459: Creating a Rogue Certification Authority Certificate
An adversary exploits a weakness resulting from using a hashing algorithm with weak collision resistance to generate certificate signing requests (CSR) that contain collision blocks in their "to be signed" parts. The adversary submits one CSR to be signed by a trusted certificate authority then uses the signed blob to make a second certificate appear signed by said certificate authority. Due to the hash collision, both certificates, though different, hash to the same value and so the signed blob works just as well in the second certificate. The net effect is that the adversary's second X.509 certificate, which the Certification Authority has never seen, is now signed and validated by that Certification Authority.
CAPEC-475: Signature Spoofing by Improper Validation
An adversary exploits a cryptographic weakness in the signature verification algorithm implementation to generate a valid signature without knowing the key.