CWE-295
AllowedImproper Certificate Validation
Abstraction: Base · Status: Draft
The product does not validate, or incorrectly validates, a certificate.
2177 vulnerabilities reference this CWE, most recent first.
GHSA-J3QW-G67Q-7M64
Vulnerability from github – Published: 2022-09-25 00:00 – Updated: 2022-09-30 04:26Apache Pulsar Brokers and Proxies create an internal Pulsar Admin Client that does not verify peer TLS certificates, even when tlsAllowInsecureConnection is disabled via configuration. The Pulsar Admin Client's intra-cluster and geo-replication HTTPS connections are vulnerable to man in the middle attacks, which could leak authentication data, configuration data, and any other data sent by these clients. An attacker can only take advantage of this vulnerability by taking control of a machine 'between' the client and the server. The attacker must then actively manipulate traffic to perform the attack. This issue affects Apache Pulsar Broker and Proxy versions 2.7.0 to 2.7.4; 2.8.0 to 2.8.3; 2.9.0 to 2.9.2; 2.10.0; 2.6.4 and earlier.
{
"affected": [
{
"package": {
"ecosystem": "Maven",
"name": "org.apache.pulsar:pulsar-broker"
},
"ranges": [
{
"events": [
{
"introduced": "0"
},
{
"fixed": "2.7.5"
}
],
"type": "ECOSYSTEM"
}
]
},
{
"package": {
"ecosystem": "Maven",
"name": "org.apache.pulsar:pulsar-proxy"
},
"ranges": [
{
"events": [
{
"introduced": "0"
},
{
"fixed": "2.7.5"
}
],
"type": "ECOSYSTEM"
}
]
},
{
"package": {
"ecosystem": "Maven",
"name": "org.apache.pulsar:pulsar-broker"
},
"ranges": [
{
"events": [
{
"introduced": "2.8.0"
},
{
"fixed": "2.8.4"
}
],
"type": "ECOSYSTEM"
}
]
},
{
"package": {
"ecosystem": "Maven",
"name": "org.apache.pulsar:pulsar-proxy"
},
"ranges": [
{
"events": [
{
"introduced": "2.8.0"
},
{
"fixed": "2.8.4"
}
],
"type": "ECOSYSTEM"
}
]
},
{
"package": {
"ecosystem": "Maven",
"name": "org.apache.pulsar:pulsar-broker"
},
"ranges": [
{
"events": [
{
"introduced": "2.9.0"
},
{
"fixed": "2.9.3"
}
],
"type": "ECOSYSTEM"
}
]
},
{
"package": {
"ecosystem": "Maven",
"name": "org.apache.pulsar:pulsar-proxy"
},
"ranges": [
{
"events": [
{
"introduced": "2.9.0"
},
{
"fixed": "2.9.3"
}
],
"type": "ECOSYSTEM"
}
]
},
{
"package": {
"ecosystem": "Maven",
"name": "org.apache.pulsar:pulsar-broker"
},
"ranges": [
{
"events": [
{
"introduced": "2.10.0"
},
{
"fixed": "2.10.1"
}
],
"type": "ECOSYSTEM"
}
],
"versions": [
"2.10.0"
]
},
{
"package": {
"ecosystem": "Maven",
"name": "org.apache.pulsar:pulsar-proxy"
},
"ranges": [
{
"events": [
{
"introduced": "2.10.0"
},
{
"fixed": "2.10.1"
}
],
"type": "ECOSYSTEM"
}
],
"versions": [
"2.10.0"
]
}
],
"aliases": [
"CVE-2022-33683"
],
"database_specific": {
"cwe_ids": [
"CWE-295"
],
"github_reviewed": true,
"github_reviewed_at": "2022-09-30T04:26:00Z",
"nvd_published_at": "2022-09-23T10:15:00Z",
"severity": "MODERATE"
},
"details": "Apache Pulsar Brokers and Proxies create an internal Pulsar Admin Client that does not verify peer TLS certificates, even when tlsAllowInsecureConnection is disabled via configuration. The Pulsar Admin Client\u0027s intra-cluster and geo-replication HTTPS connections are vulnerable to man in the middle attacks, which could leak authentication data, configuration data, and any other data sent by these clients. An attacker can only take advantage of this vulnerability by taking control of a machine \u0027between\u0027 the client and the server. The attacker must then actively manipulate traffic to perform the attack. This issue affects Apache Pulsar Broker and Proxy versions 2.7.0 to 2.7.4; 2.8.0 to 2.8.3; 2.9.0 to 2.9.2; 2.10.0; 2.6.4 and earlier.",
"id": "GHSA-j3qw-g67q-7m64",
"modified": "2022-09-30T04:26:00Z",
"published": "2022-09-25T00:00:27Z",
"references": [
{
"type": "ADVISORY",
"url": "https://nvd.nist.gov/vuln/detail/CVE-2022-33683"
},
{
"type": "WEB",
"url": "https://lists.apache.org/thread/42v5rsxj36r3nhfxhmhb2x12r5jmvx3x"
}
],
"schema_version": "1.4.0",
"severity": [
{
"score": "CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:N/A:N",
"type": "CVSS_V3"
}
],
"summary": "Apache Pulsar Brokers and Proxies vulnerable to Improper Certificate Validation"
}
GHSA-J3R3-Q9V5-GG3H
Vulnerability from github – Published: 2025-11-17 18:30 – Updated: 2025-11-17 18:30GoSign Desktop through 2.4.1 disables TLS certificate validation when configured to use a proxy server. This can be problematic if the GoSign Desktop user selects an arbitrary proxy server without consideration of whether outbound HTTPS connections from the proxy server to Internet servers succeed even for untrusted or invalid server certificates. In this scenario (which is outside of the product's design objectives), integrity protection could be bypassed. In typical cases of a proxy server for outbound HTTPS traffic from an enterprise, those connections would not succeed. (Admittedly, the usual expectation is that a client application is configured to trust an enterprise CA and does not set SSL_VERIFY_NONE.) Also, it is of course unsafe to place ~/.gosign in the home directory of an untrusted user and then have other users execute downloaded files.
{
"affected": [],
"aliases": [
"CVE-2025-65083"
],
"database_specific": {
"cwe_ids": [
"CWE-295"
],
"github_reviewed": false,
"github_reviewed_at": null,
"nvd_published_at": "2025-11-17T16:15:51Z",
"severity": "LOW"
},
"details": "GoSign Desktop through 2.4.1 disables TLS certificate validation when configured to use a proxy server. This can be problematic if the GoSign Desktop user selects an arbitrary proxy server without consideration of whether outbound HTTPS connections from the proxy server to Internet servers succeed even for untrusted or invalid server certificates. In this scenario (which is outside of the product\u0027s design objectives), integrity protection could be bypassed. In typical cases of a proxy server for outbound HTTPS traffic from an enterprise, those connections would not succeed. (Admittedly, the usual expectation is that a client application is configured to trust an enterprise CA and does not set SSL_VERIFY_NONE.) Also, it is of course unsafe to place ~/.gosign in the home directory of an untrusted user and then have other users execute downloaded files.",
"id": "GHSA-j3r3-q9v5-gg3h",
"modified": "2025-11-17T18:30:30Z",
"published": "2025-11-17T18:30:30Z",
"references": [
{
"type": "ADVISORY",
"url": "https://nvd.nist.gov/vuln/detail/CVE-2025-65083"
},
{
"type": "WEB",
"url": "https://securityaffairs.com/184672/hacking/multiple-vulnerabilities-in-gosign-desktop-lead-to-remote-code-execution.html"
},
{
"type": "WEB",
"url": "https://www.firma.infocert.it/prodotti/gosign"
}
],
"schema_version": "1.4.0",
"severity": [
{
"score": "CVSS:3.1/AV:L/AC:H/PR:N/UI:N/S:C/C:N/I:L/A:N",
"type": "CVSS_V3"
}
]
}
GHSA-J443-WCQQ-XPRH
Vulnerability from github – Published: 2026-03-11 00:32 – Updated: 2026-03-11 00:32Summary
A critical vulnerability has been identified at https://security.snyk.io/package/linux/chainguard:latest/terraform-provider-sendgrid, associated with the underlying Go version.
If the server's TLS configuration is mutated between connections — for example, a CA is removed from the trusted list via Config.Clone() combined with modification or GetConfigForClient — the resumed handshake still succeeds using the cached session. The certificate is not re-checked against the updated CA list.
As a result, a client whose CA was revoked or removed between the first and second connection could still establish a connection on the resumed session.
Details
If the server's TLS configuration is mutated between connections — for example, a CA is removed from the trusted list via Config.Clone() combined with modification or GetConfigForClient — the resumed handshake still succeeds using the cached session. The certificate is not re-checked against the updated CA list.
Consequently, a client whose CA was revoked or removed between the first and second connection could still establish a connection on the resumed session.
{
"affected": [
{
"package": {
"ecosystem": "Go",
"name": "github.com/arslanbekov/terraform-provider-sendgrid"
},
"ranges": [
{
"events": [
{
"introduced": "0"
},
{
"last_affected": "1.1.3-0.20250606002314-b4a2dfeb7b0f"
}
],
"type": "ECOSYSTEM"
}
]
}
],
"aliases": [],
"database_specific": {
"cwe_ids": [
"CWE-295"
],
"github_reviewed": true,
"github_reviewed_at": "2026-03-11T00:32:49Z",
"nvd_published_at": null,
"severity": "CRITICAL"
},
"details": "### Summary\n\nA critical vulnerability has been identified at https://security.snyk.io/package/linux/chainguard:latest/terraform-provider-sendgrid, associated with the underlying Go version.\n\nIf the server\u0027s TLS configuration is mutated between connections \u2014 for example, a CA is removed from the trusted list via `Config.Clone()` combined with modification or `GetConfigForClient` \u2014 the resumed handshake still succeeds using the cached session. The certificate is not re-checked against the updated CA list.\n\nAs a result, a client whose CA was revoked or removed between the first and second connection could still establish a connection on the resumed session.\n\n### Details\n\nIf the server\u0027s TLS configuration is mutated between connections \u2014 for example, a CA is removed from the trusted list via `Config.Clone()` combined with modification or `GetConfigForClient` \u2014 the resumed handshake still succeeds using the cached session. The certificate is not re-checked against the updated CA list.\n\nConsequently, a client whose CA was revoked or removed between the first and second connection could still establish a connection on the resumed session.",
"id": "GHSA-j443-wcqq-xprh",
"modified": "2026-03-11T00:32:49Z",
"published": "2026-03-11T00:32:49Z",
"references": [
{
"type": "WEB",
"url": "https://github.com/arslanbekov/terraform-provider-sendgrid/security/advisories/GHSA-j443-wcqq-xprh"
},
{
"type": "ADVISORY",
"url": "https://github.com/advisories/GHSA-h355-32pf-p2xm"
},
{
"type": "PACKAGE",
"url": "https://github.com/arslanbekov/terraform-provider-sendgrid"
},
{
"type": "WEB",
"url": "https://security.snyk.io/vuln/SNYK-CHAINGUARDLATEST-TERRAFORMPROVIDERSENDGRID-15265295"
}
],
"schema_version": "1.4.0",
"severity": [
{
"score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:H",
"type": "CVSS_V3"
}
],
"summary": "Terraform Provider for SendGrid: TLS Session Resumption Bypasses Certificate Authority Trust Store Modifications in Go"
}
GHSA-J4X4-2CC8-7274
Vulnerability from github – Published: 2023-04-15 00:30 – Updated: 2024-04-04 03:28x509/x509_verify.c in LibreSSL before 3.4.2, and OpenBSD before 7.0 errata 006, allows authentication bypass because an error for an unverified certificate chain is sometimes discarded.
{
"affected": [],
"aliases": [
"CVE-2021-46880"
],
"database_specific": {
"cwe_ids": [
"CWE-295"
],
"github_reviewed": false,
"github_reviewed_at": null,
"nvd_published_at": "2023-04-15T00:15:00Z",
"severity": "CRITICAL"
},
"details": "x509/x509_verify.c in LibreSSL before 3.4.2, and OpenBSD before 7.0 errata 006, allows authentication bypass because an error for an unverified certificate chain is sometimes discarded.",
"id": "GHSA-j4x4-2cc8-7274",
"modified": "2024-04-04T03:28:55Z",
"published": "2023-04-15T00:30:35Z",
"references": [
{
"type": "ADVISORY",
"url": "https://nvd.nist.gov/vuln/detail/CVE-2021-46880"
},
{
"type": "WEB",
"url": "https://github.com/openbsd/src/commit/3f851282810fa0ab4b90b3b1ecec2e8717ef16f8"
},
{
"type": "WEB",
"url": "https://ftp.openbsd.org/pub/OpenBSD/LibreSSL/libressl-3.4.2-relnotes.txt"
},
{
"type": "WEB",
"url": "https://ftp.openbsd.org/pub/OpenBSD/patches/7.0/common/006_x509.patch.sig"
},
{
"type": "WEB",
"url": "https://security.netapp.com/advisory/ntap-20230517-0006"
}
],
"schema_version": "1.4.0",
"severity": [
{
"score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H",
"type": "CVSS_V3"
}
]
}
GHSA-J568-5HJM-GQ5G
Vulnerability from github – Published: 2024-07-26 21:31 – Updated: 2024-07-26 21:31An improper validation vulnerability was reported in the Lenovo Tab K10 that could allow a specially crafted application to keep the device on.
{
"affected": [],
"aliases": [
"CVE-2024-4786"
],
"database_specific": {
"cwe_ids": [
"CWE-295"
],
"github_reviewed": false,
"github_reviewed_at": null,
"nvd_published_at": "2024-07-26T20:15:05Z",
"severity": "LOW"
},
"details": "An improper validation vulnerability was reported in the Lenovo Tab K10 that could allow a specially crafted application to keep the device on.",
"id": "GHSA-j568-5hjm-gq5g",
"modified": "2024-07-26T21:31:16Z",
"published": "2024-07-26T21:31:16Z",
"references": [
{
"type": "ADVISORY",
"url": "https://nvd.nist.gov/vuln/detail/CVE-2024-4786"
},
{
"type": "WEB",
"url": "https://support.lenovo.com/us/en/product_security/LEN-158501"
}
],
"schema_version": "1.4.0",
"severity": [
{
"score": "CVSS:3.1/AV:L/AC:L/PR:L/UI:R/S:U/C:N/I:N/A:L",
"type": "CVSS_V3"
}
]
}
GHSA-J577-G4XC-MPJ3
Vulnerability from github – Published: 2022-05-14 03:42 – Updated: 2022-05-14 03:42The GUI component (aka PulseUI) in Pulse Secure Desktop Linux clients before PULSE5.2R9.2 and 5.3.x before PULSE5.3R4.2 does not perform strict SSL Certificate Validation. This can lead to the manipulation of the Pulse Connection set.
{
"affected": [],
"aliases": [
"CVE-2018-6374"
],
"database_specific": {
"cwe_ids": [
"CWE-295"
],
"github_reviewed": false,
"github_reviewed_at": null,
"nvd_published_at": "2018-01-31T21:29:00Z",
"severity": "MODERATE"
},
"details": "The GUI component (aka PulseUI) in Pulse Secure Desktop Linux clients before PULSE5.2R9.2 and 5.3.x before PULSE5.3R4.2 does not perform strict SSL Certificate Validation. This can lead to the manipulation of the Pulse Connection set.",
"id": "GHSA-j577-g4xc-mpj3",
"modified": "2022-05-14T03:42:27Z",
"published": "2022-05-14T03:42:27Z",
"references": [
{
"type": "ADVISORY",
"url": "https://nvd.nist.gov/vuln/detail/CVE-2018-6374"
},
{
"type": "WEB",
"url": "http://kb.pulsesecure.net/articles/Pulse_Security_Advisories/SA43620"
},
{
"type": "WEB",
"url": "http://www.securityfocus.com/bid/102908"
}
],
"schema_version": "1.4.0",
"severity": [
{
"score": "CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:L",
"type": "CVSS_V3"
}
]
}
GHSA-J57H-G9HV-4P44
Vulnerability from github – Published: 2025-02-01 09:30 – Updated: 2025-02-01 09:30An Improper Certificate Validation on UniFi OS devices, with Identity Enterprise configured, could allow a malicious actor to execute a man-in-the-middle (MitM) attack during application update.
{
"affected": [],
"aliases": [
"CVE-2025-23091"
],
"database_specific": {
"cwe_ids": [
"CWE-295"
],
"github_reviewed": false,
"github_reviewed_at": null,
"nvd_published_at": "2025-02-01T07:15:08Z",
"severity": "MODERATE"
},
"details": "An Improper Certificate Validation on UniFi OS devices, with Identity Enterprise configured, could allow a malicious actor to execute a man-in-the-middle (MitM) attack during application update.",
"id": "GHSA-j57h-g9hv-4p44",
"modified": "2025-02-01T09:30:28Z",
"published": "2025-02-01T09:30:28Z",
"references": [
{
"type": "ADVISORY",
"url": "https://nvd.nist.gov/vuln/detail/CVE-2025-23091"
},
{
"type": "WEB",
"url": "https://community.ui.com/releases/Security-Advisory-Bulletin-045-045/6011bc61-f2eb-457f-b71d-755703817aaf"
}
],
"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-J597-VWRG-G7QG
Vulnerability from github – Published: 2026-08-10 09:31 – Updated: 2026-08-10 09:31DEEBOT PRO M1 and DEEBOT PRO K1VAC use wget command with server certificate validation disabled. A man-in-the-middle attack may allow to obtain and/or alter communications of the affected products. As a result, arbitrary code may be executed with the administrative privilege.
{
"affected": [],
"aliases": [
"CVE-2026-66406"
],
"database_specific": {
"cwe_ids": [
"CWE-295"
],
"github_reviewed": false,
"github_reviewed_at": null,
"nvd_published_at": "2026-08-10T09:17:22Z",
"severity": "LOW"
},
"details": "DEEBOT PRO M1 and DEEBOT PRO K1VAC use wget command with server certificate validation disabled.\nA man-in-the-middle attack may allow to obtain and/or alter communications of the affected products. As a result, arbitrary code may be executed with the administrative privilege.",
"id": "GHSA-j597-vwrg-g7qg",
"modified": "2026-08-10T09:31:23Z",
"published": "2026-08-10T09:31:23Z",
"references": [
{
"type": "ADVISORY",
"url": "https://nvd.nist.gov/vuln/detail/CVE-2026-66406"
},
{
"type": "WEB",
"url": "https://jvn.jp/en/vu/JVNVU92804348"
},
{
"type": "WEB",
"url": "https://robot.hellohas.co.jp/news/update_20260331"
}
],
"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"
},
{
"score": "CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:P/VC:L/VI:L/VA:N/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X",
"type": "CVSS_V4"
}
]
}
GHSA-J639-F4GQ-49CP
Vulnerability from github – Published: 2025-04-17 12:30 – Updated: 2025-04-17 12:30Dell ECS version 3.8.1.4 and prior contain an Improper Certificate Validation vulnerability. An unauthenticated attacker with adjacent network access could potentially exploit this vulnerability, leading to Information disclosure.
{
"affected": [],
"aliases": [
"CVE-2025-26478"
],
"database_specific": {
"cwe_ids": [
"CWE-295"
],
"github_reviewed": false,
"github_reviewed_at": null,
"nvd_published_at": "2025-04-17T12:15:15Z",
"severity": "LOW"
},
"details": "Dell ECS version 3.8.1.4 and prior contain an Improper Certificate Validation vulnerability. An unauthenticated attacker with adjacent network access could potentially exploit this vulnerability, leading to Information disclosure.",
"id": "GHSA-j639-f4gq-49cp",
"modified": "2025-04-17T12:30:32Z",
"published": "2025-04-17T12:30:32Z",
"references": [
{
"type": "ADVISORY",
"url": "https://nvd.nist.gov/vuln/detail/CVE-2025-26478"
},
{
"type": "WEB",
"url": "https://www.dell.com/support/kbdoc/en-in/000300068/dsa-2025-097-security-update-for-dell-objectscale-4-0-multiple-vulnerabilities"
}
],
"schema_version": "1.4.0",
"severity": [
{
"score": "CVSS:3.1/AV:A/AC:H/PR:N/UI:N/S:U/C:L/I:N/A:N",
"type": "CVSS_V3"
}
]
}
GHSA-J63F-H5JJ-QRF5
Vulnerability from github – Published: 2026-08-03 21:31 – Updated: 2026-08-03 21:31Emlog Pro through 2.6.23 contains a disabled TLS certificate validation vulnerability in include/service/ai.php that allows network-adjacent attackers to intercept outbound HTTPS requests to configured LLM providers by presenting arbitrary TLS certificates, as CURLOPT_SSL_VERIFYPEER and CURLOPT_SSL_VERIFYHOST are unconditionally disabled across sendStream(), sendImageRequest(), send(), and fetchSearchHtml() with no option to re-enable verification. Attackers can perform man-in-the-middle interception to extract Authorization Bearer API keys from every AI request and inject crafted AI responses that may be acted upon by the tool-call execution pipeline, including the query_database and update_config tool handlers.
{
"affected": [],
"aliases": [
"CVE-2026-67598"
],
"database_specific": {
"cwe_ids": [
"CWE-295"
],
"github_reviewed": false,
"github_reviewed_at": null,
"nvd_published_at": "2026-08-03T20:17:27Z",
"severity": "CRITICAL"
},
"details": "Emlog Pro through 2.6.23 contains a disabled TLS certificate validation vulnerability in include/service/ai.php that allows network-adjacent attackers to intercept outbound HTTPS requests to configured LLM providers by presenting arbitrary TLS certificates, as CURLOPT_SSL_VERIFYPEER and CURLOPT_SSL_VERIFYHOST are unconditionally disabled across sendStream(), sendImageRequest(), send(), and fetchSearchHtml() with no option to re-enable verification. Attackers can perform man-in-the-middle interception to extract Authorization Bearer API keys from every AI request and inject crafted AI responses that may be acted upon by the tool-call execution pipeline, including the query_database and update_config tool handlers.",
"id": "GHSA-j63f-h5jj-qrf5",
"modified": "2026-08-03T21:31:37Z",
"published": "2026-08-03T21:31:37Z",
"references": [
{
"type": "WEB",
"url": "https://github.com/emlog/emlog/security/advisories/GHSA-hf85-99vj-m4c5"
},
{
"type": "ADVISORY",
"url": "https://nvd.nist.gov/vuln/detail/CVE-2026-67598"
},
{
"type": "WEB",
"url": "https://www.vulncheck.com/advisories/emlog-pro-tls-certificate-validation-disabled-in-ai-php"
}
],
"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"
},
{
"score": "CVSS:4.0/AV:N/AC:H/AT:N/PR:N/UI:N/VC:H/VI:H/VA:N/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X",
"type": "CVSS_V4"
}
]
}
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.