CVE-2026-96770 (GCVE-0-2026-96770)
Vulnerability from cvelistv5 – Published: 2026-09-23 18:58 – Updated: 2026-09-23 19:36
VLAI
EPSS
VEX
Title
s2s-proxy accepts untrusted client certificates
Summary
All published s2s-proxy versions through 0.2.2 are affected. In versions 0.1.16 through 0.2.2, TLS server listeners use Go's RequireAnyClientCert mode when skipCAVerification is false. This mode checks that the client holds the certificate's private key but does not verify the certificate against the configured CA. An attacker can therefore use a self-signed certificate and key to establish a TLS and yamux connection, then invoke RPCs allowed by the proxy's configuration and Temporal credentials. No certificate or private key trusted by the deployment, and no Temporal credential, is required.
Severity
SSVC
Exploitation: none
Automatable: yes
Technical Impact: total
CISA Coordinator · CISA-ADP (v2.0.3)
Decision recorded 2026-09-23 19:36 UTC
CWE
- CWE-296 - Improper Following of a Certificate's Chain of Trust
Assigner
References
5 references
Impacted products
1 product
| Vendor | Product | Version | CPE status | |
|---|---|---|---|---|
| Temporal Technologies, Inc. | s2s-proxy |
Affected:
0.0.1-alpha , ≤ 0.2.2
(semver)
|
guessed |
{
"containers": {
"adp": [
{
"metrics": [
{
"other": {
"content": {
"id": "CVE-2026-96770",
"options": [
{
"Exploitation": "none"
},
{
"Automatable": "yes"
},
{
"Technical Impact": "total"
}
],
"role": "CISA Coordinator",
"timestamp": "2026-09-23T19:36:07.279659Z",
"version": "2.0.3"
},
"type": "ssvc"
}
}
],
"providerMetadata": {
"dateUpdated": "2026-09-23T19:36:12.488Z",
"orgId": "134c704f-9b21-4f2e-91b3-4a467353bcc0",
"shortName": "CISA-ADP"
},
"title": "CISA ADP Vulnrichment"
}
],
"cna": {
"affected": [
{
"collectionURL": "https://pkg.go.dev",
"defaultStatus": "unaffected",
"packageName": "github.com/temporalio/s2s-proxy",
"product": "s2s-proxy",
"programFiles": [
"encryption/tls.go"
],
"programRoutines": [
{
"name": "GetServerTLSConfig"
}
],
"repo": "https://github.com/temporalio/s2s-proxy",
"vendor": "Temporal Technologies, Inc.",
"versions": [
{
"lessThanOrEqual": "0.2.2",
"status": "affected",
"version": "0.0.1-alpha",
"versionType": "semver"
}
]
}
],
"configurations": [
{
"lang": "en",
"supportingMedia": [
{
"base64": false,
"type": "text/html",
"value": "\u003cp\u003eExploitation requires network access to an affected TLS server listener configured with skipCAVerification set to false. Available RPCs and namespaces are limited by the proxy\u0027s allowlists and the permissions granted to its Temporal credentials.\u003c/p\u003e"
}
],
"value": "Exploitation requires network access to an affected TLS server listener configured with skipCAVerification set to false. Available RPCs and namespaces are limited by the proxy\u0027s allowlists and the permissions granted to its Temporal credentials."
}
],
"credits": [
{
"lang": "en",
"type": "finder",
"value": "Praetorian, who reported this issue responsibly to Temporal Technologies"
}
],
"descriptions": [
{
"lang": "en",
"supportingMedia": [
{
"base64": false,
"type": "text/html",
"value": "\u003cp\u003eAll published s2s-proxy versions through 0.2.2 are affected. In versions 0.1.16 through 0.2.2, TLS server listeners use Go\u0027s RequireAnyClientCert mode when skipCAVerification is false. This mode checks that the client holds the certificate\u0027s private key but does not verify the certificate against the configured CA. An attacker can therefore use a self-signed certificate and key to establish a TLS and yamux connection, then invoke RPCs allowed by the proxy\u0027s configuration and Temporal credentials. No certificate or private key trusted by the deployment, and no Temporal credential, is required.\u003c/p\u003e"
}
],
"value": "All published s2s-proxy versions through 0.2.2 are affected. In versions 0.1.16 through 0.2.2, TLS server listeners use Go\u0027s RequireAnyClientCert mode when skipCAVerification is false. This mode checks that the client holds the certificate\u0027s private key but does not verify the certificate against the configured CA. An attacker can therefore use a self-signed certificate and key to establish a TLS and yamux connection, then invoke RPCs allowed by the proxy\u0027s configuration and Temporal credentials. No certificate or private key trusted by the deployment, and no Temporal credential, is required."
}
],
"impacts": [
{
"descriptions": [
{
"lang": "en",
"value": "An attacker who can reach the listener can connect as a trusted peer with a self-signed certificate and invoke allowed RPCs through the proxy\u0027s Temporal credentials. Impact depends on the RPC and namespace allowlists and the permissions granted to those credentials. A permissive deployment can expose workflow data or allow workflow changes and deletion. Data protected by a Payload Codec remains encrypted unless the attacker can also access the customer\u0027s Codec Server or encryption keys."
}
]
}
],
"metrics": [
{
"cvssV4_0": {
"Automatable": "NOT_DEFINED",
"Recovery": "NOT_DEFINED",
"Safety": "NOT_DEFINED",
"attackComplexity": "LOW",
"attackRequirements": "NONE",
"attackVector": "NETWORK",
"baseScore": 9.3,
"baseSeverity": "CRITICAL",
"exploitMaturity": "NOT_DEFINED",
"privilegesRequired": "NONE",
"providerUrgency": "NOT_DEFINED",
"subAvailabilityImpact": "HIGH",
"subConfidentialityImpact": "HIGH",
"subIntegrityImpact": "HIGH",
"userInteraction": "NONE",
"valueDensity": "NOT_DEFINED",
"vectorString": "CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:H/VA:N/SC:H/SI:H/SA:H",
"version": "4.0",
"vulnAvailabilityImpact": "NONE",
"vulnConfidentialityImpact": "NONE",
"vulnIntegrityImpact": "HIGH",
"vulnerabilityResponseEffort": "NOT_DEFINED"
},
"format": "CVSS",
"scenarios": [
{
"lang": "en",
"value": "GENERAL"
}
]
}
],
"problemTypes": [
{
"descriptions": [
{
"cweId": "CWE-296",
"description": "CWE-296: Improper Following of a Certificate\u0027s Chain of Trust",
"lang": "en",
"type": "CWE"
}
]
}
],
"providerMetadata": {
"dateUpdated": "2026-09-23T18:58:46.233Z",
"orgId": "61241ed8-fa44-4f23-92db-b8c443751968",
"shortName": "Temporal"
},
"references": [
{
"name": "Affected TLS server configuration in s2s-proxy 0.2.2",
"tags": [
"product"
],
"url": "https://github.com/temporalio/s2s-proxy/blob/v0.2.2/encryption/tls.go#L47-L62"
},
{
"name": "Change that introduced the affected certificate verification mode",
"tags": [
"product"
],
"url": "https://github.com/temporalio/s2s-proxy/commit/d100c2258dbc37d7df51298ea045315f36c7eb3b"
},
{
"name": "Fix pull request",
"tags": [
"patch"
],
"url": "https://github.com/temporalio/s2s-proxy/pull/296"
},
{
"name": "Fix commit",
"tags": [
"patch"
],
"url": "https://github.com/temporalio/s2s-proxy/commit/f1dc6b9a3919d37e82545ab461cbe6bb62618d3c"
},
{
"name": "Temporal Payload Codec and Codec Server documentation",
"tags": [
"product"
],
"url": "https://docs.temporal.io/production-deployment/data-encryption#codec-server-setup"
}
],
"solutions": [
{
"lang": "en",
"supportingMedia": [
{
"base64": false,
"type": "text/html",
"value": "\u003cp\u003eThe fix is expected in version 0.2.3. Upgrade to version 0.2.3 or later when available.\u003c/p\u003e"
}
],
"value": "The fix is expected in version 0.2.3. Upgrade to version 0.2.3 or later when available."
}
],
"source": {
"discovery": "EXTERNAL"
},
"title": "s2s-proxy accepts untrusted client certificates",
"workarounds": [
{
"lang": "en",
"supportingMedia": [
{
"base64": false,
"type": "text/html",
"value": "\u003cp\u003eRestrict the listener to known peer addresses or a private network, or use a TLS terminator that verifies client certificates against the intended CA. These controls reduce exposure but do not fix the proxy defect.\u003c/p\u003e"
}
],
"value": "Restrict the listener to known peer addresses or a private network, or use a TLS terminator that verifies client certificates against the intended CA. These controls reduce exposure but do not fix the proxy defect."
}
]
}
},
"cveMetadata": {
"assignerOrgId": "61241ed8-fa44-4f23-92db-b8c443751968",
"assignerShortName": "Temporal",
"cveId": "CVE-2026-96770",
"datePublished": "2026-09-23T18:58:46.233Z",
"dateReserved": "2026-09-23T16:06:36.077Z",
"dateUpdated": "2026-09-23T19:36:12.488Z",
"state": "PUBLISHED"
},
"dataType": "CVE_RECORD",
"dataVersion": "5.2",
"vulnerability-lookup:meta": {
"epss": {
"cve": "CVE-2026-96770",
"date": "2026-09-24",
"epss": "0.00254",
"percentile": "0.15102"
},
"nvd": {
"cve": {
"affected": [
{
"affectedData": [
{
"collectionURL": "https://pkg.go.dev",
"defaultStatus": "unaffected",
"packageName": "github.com/temporalio/s2s-proxy",
"product": "s2s-proxy",
"programFiles": [
"encryption/tls.go"
],
"programRoutines": [
{
"name": "GetServerTLSConfig"
}
],
"repo": "https://github.com/temporalio/s2s-proxy",
"vendor": "Temporal Technologies, Inc.",
"versions": [
{
"lessThanOrEqual": "0.2.2",
"status": "affected",
"version": "0.0.1-alpha",
"versionType": "semver"
}
]
}
],
"source": "security@temporal.io"
}
],
"cveTags": [],
"descriptions": [
{
"lang": "en",
"value": "All published s2s-proxy versions through 0.2.2 are affected. In versions 0.1.16 through 0.2.2, TLS server listeners use Go\u0027s RequireAnyClientCert mode when skipCAVerification is false. This mode checks that the client holds the certificate\u0027s private key but does not verify the certificate against the configured CA. An attacker can therefore use a self-signed certificate and key to establish a TLS and yamux connection, then invoke RPCs allowed by the proxy\u0027s configuration and Temporal credentials. No certificate or private key trusted by the deployment, and no Temporal credential, is required."
}
],
"id": "CVE-2026-96770",
"lastModified": "2026-09-24T20:43:32.537",
"metrics": {
"cvssMetricV40": [
{
"cvssData": {
"Automatable": "NOT_DEFINED",
"Recovery": "NOT_DEFINED",
"Safety": "NOT_DEFINED",
"attackComplexity": "LOW",
"attackRequirements": "NONE",
"attackVector": "NETWORK",
"availabilityRequirement": "NOT_DEFINED",
"baseScore": 9.3,
"baseSeverity": "CRITICAL",
"confidentialityRequirement": "NOT_DEFINED",
"exploitMaturity": "NOT_DEFINED",
"integrityRequirement": "NOT_DEFINED",
"modifiedAttackComplexity": "NOT_DEFINED",
"modifiedAttackRequirements": "NOT_DEFINED",
"modifiedAttackVector": "NOT_DEFINED",
"modifiedPrivilegesRequired": "NOT_DEFINED",
"modifiedSubAvailabilityImpact": "NOT_DEFINED",
"modifiedSubConfidentialityImpact": "NOT_DEFINED",
"modifiedSubIntegrityImpact": "NOT_DEFINED",
"modifiedUserInteraction": "NOT_DEFINED",
"modifiedVulnAvailabilityImpact": "NOT_DEFINED",
"modifiedVulnConfidentialityImpact": "NOT_DEFINED",
"modifiedVulnIntegrityImpact": "NOT_DEFINED",
"privilegesRequired": "NONE",
"providerUrgency": "NOT_DEFINED",
"subAvailabilityImpact": "HIGH",
"subConfidentialityImpact": "HIGH",
"subIntegrityImpact": "HIGH",
"userInteraction": "NONE",
"valueDensity": "NOT_DEFINED",
"vectorString": "CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:H/VA:N/SC:H/SI:H/SA:H/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",
"version": "4.0",
"vulnAvailabilityImpact": "NONE",
"vulnConfidentialityImpact": "NONE",
"vulnIntegrityImpact": "HIGH",
"vulnerabilityResponseEffort": "NOT_DEFINED"
},
"source": "security@temporal.io",
"type": "Secondary"
}
],
"ssvcV203": [
{
"source": "134c704f-9b21-4f2e-91b3-4a467353bcc0",
"ssvcData": {
"id": "CVE-2026-96770",
"options": [
{
"exploitation": "none"
},
{
"automatable": "yes"
},
{
"technicalImpact": "total"
}
],
"role": "CISA Coordinator",
"timestamp": "2026-09-23T19:36:07.279659Z",
"version": "2.0.3"
}
}
]
},
"published": "2026-09-23T19:19:55.013",
"references": [
{
"source": "security@temporal.io",
"url": "https://docs.temporal.io/production-deployment/data-encryption#codec-server-setup"
},
{
"source": "security@temporal.io",
"url": "https://github.com/temporalio/s2s-proxy/blob/v0.2.2/encryption/tls.go#L47-L62"
},
{
"source": "security@temporal.io",
"url": "https://github.com/temporalio/s2s-proxy/commit/d100c2258dbc37d7df51298ea045315f36c7eb3b"
},
{
"source": "security@temporal.io",
"url": "https://github.com/temporalio/s2s-proxy/commit/f1dc6b9a3919d37e82545ab461cbe6bb62618d3c"
},
{
"source": "security@temporal.io",
"url": "https://github.com/temporalio/s2s-proxy/pull/296"
}
],
"sourceIdentifier": "security@temporal.io",
"vulnStatus": "Deferred",
"weaknesses": [
{
"description": [
{
"lang": "en",
"value": "CWE-296"
}
],
"source": "security@temporal.io",
"type": "Secondary"
}
]
}
},
"vulnrichment": {
"containers": {
"adp": [
{
"metrics": [
{
"other": {
"content": {
"id": "CVE-2026-96770",
"options": [
{
"Exploitation": "none"
},
{
"Automatable": "yes"
},
{
"Technical Impact": "total"
}
],
"role": "CISA Coordinator",
"timestamp": "2026-09-23T19:36:07.279659Z",
"version": "2.0.3"
},
"type": "ssvc"
}
}
],
"providerMetadata": {
"dateUpdated": "2026-09-23T19:36:10.230Z",
"orgId": "134c704f-9b21-4f2e-91b3-4a467353bcc0",
"shortName": "CISA-ADP"
},
"title": "CISA ADP Vulnrichment"
}
],
"cna": {
"affected": [
{
"collectionURL": "https://pkg.go.dev",
"defaultStatus": "unaffected",
"packageName": "github.com/temporalio/s2s-proxy",
"product": "s2s-proxy",
"programFiles": [
"encryption/tls.go"
],
"programRoutines": [
{
"name": "GetServerTLSConfig"
}
],
"repo": "https://github.com/temporalio/s2s-proxy",
"vendor": "Temporal Technologies, Inc.",
"versions": [
{
"lessThanOrEqual": "0.2.2",
"status": "affected",
"version": "0.0.1-alpha",
"versionType": "semver"
}
]
}
],
"configurations": [
{
"lang": "en",
"supportingMedia": [
{
"base64": false,
"type": "text/html",
"value": "\u003cp\u003eExploitation requires network access to an affected TLS server listener configured with skipCAVerification set to false. Available RPCs and namespaces are limited by the proxy\u0027s allowlists and the permissions granted to its Temporal credentials.\u003c/p\u003e"
}
],
"value": "Exploitation requires network access to an affected TLS server listener configured with skipCAVerification set to false. Available RPCs and namespaces are limited by the proxy\u0027s allowlists and the permissions granted to its Temporal credentials."
}
],
"credits": [
{
"lang": "en",
"type": "finder",
"value": "Praetorian, who reported this issue responsibly to Temporal Technologies"
}
],
"descriptions": [
{
"lang": "en",
"supportingMedia": [
{
"base64": false,
"type": "text/html",
"value": "\u003cp\u003eAll published s2s-proxy versions through 0.2.2 are affected. In versions 0.1.16 through 0.2.2, TLS server listeners use Go\u0027s RequireAnyClientCert mode when skipCAVerification is false. This mode checks that the client holds the certificate\u0027s private key but does not verify the certificate against the configured CA. An attacker can therefore use a self-signed certificate and key to establish a TLS and yamux connection, then invoke RPCs allowed by the proxy\u0027s configuration and Temporal credentials. No certificate or private key trusted by the deployment, and no Temporal credential, is required.\u003c/p\u003e"
}
],
"value": "All published s2s-proxy versions through 0.2.2 are affected. In versions 0.1.16 through 0.2.2, TLS server listeners use Go\u0027s RequireAnyClientCert mode when skipCAVerification is false. This mode checks that the client holds the certificate\u0027s private key but does not verify the certificate against the configured CA. An attacker can therefore use a self-signed certificate and key to establish a TLS and yamux connection, then invoke RPCs allowed by the proxy\u0027s configuration and Temporal credentials. No certificate or private key trusted by the deployment, and no Temporal credential, is required."
}
],
"impacts": [
{
"descriptions": [
{
"lang": "en",
"value": "An attacker who can reach the listener can connect as a trusted peer with a self-signed certificate and invoke allowed RPCs through the proxy\u0027s Temporal credentials. Impact depends on the RPC and namespace allowlists and the permissions granted to those credentials. A permissive deployment can expose workflow data or allow workflow changes and deletion. Data protected by a Payload Codec remains encrypted unless the attacker can also access the customer\u0027s Codec Server or encryption keys."
}
]
}
],
"metrics": [
{
"cvssV4_0": {
"Automatable": "NOT_DEFINED",
"Recovery": "NOT_DEFINED",
"Safety": "NOT_DEFINED",
"attackComplexity": "LOW",
"attackRequirements": "NONE",
"attackVector": "NETWORK",
"baseScore": 9.3,
"baseSeverity": "CRITICAL",
"exploitMaturity": "NOT_DEFINED",
"privilegesRequired": "NONE",
"providerUrgency": "NOT_DEFINED",
"subAvailabilityImpact": "HIGH",
"subConfidentialityImpact": "HIGH",
"subIntegrityImpact": "HIGH",
"userInteraction": "NONE",
"valueDensity": "NOT_DEFINED",
"vectorString": "CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:H/VA:N/SC:H/SI:H/SA:H",
"version": "4.0",
"vulnAvailabilityImpact": "NONE",
"vulnConfidentialityImpact": "NONE",
"vulnIntegrityImpact": "HIGH",
"vulnerabilityResponseEffort": "NOT_DEFINED"
},
"format": "CVSS",
"scenarios": [
{
"lang": "en",
"value": "GENERAL"
}
]
}
],
"problemTypes": [
{
"descriptions": [
{
"cweId": "CWE-296",
"description": "CWE-296: Improper Following of a Certificate\u0027s Chain of Trust",
"lang": "en",
"type": "CWE"
}
]
}
],
"providerMetadata": {
"dateUpdated": "2026-09-23T18:58:46.233Z",
"orgId": "61241ed8-fa44-4f23-92db-b8c443751968",
"shortName": "Temporal"
},
"references": [
{
"name": "Affected TLS server configuration in s2s-proxy 0.2.2",
"tags": [
"product"
],
"url": "https://github.com/temporalio/s2s-proxy/blob/v0.2.2/encryption/tls.go#L47-L62"
},
{
"name": "Change that introduced the affected certificate verification mode",
"tags": [
"product"
],
"url": "https://github.com/temporalio/s2s-proxy/commit/d100c2258dbc37d7df51298ea045315f36c7eb3b"
},
{
"name": "Fix pull request",
"tags": [
"patch"
],
"url": "https://github.com/temporalio/s2s-proxy/pull/296"
},
{
"name": "Fix commit",
"tags": [
"patch"
],
"url": "https://github.com/temporalio/s2s-proxy/commit/f1dc6b9a3919d37e82545ab461cbe6bb62618d3c"
},
{
"name": "Temporal Payload Codec and Codec Server documentation",
"tags": [
"product"
],
"url": "https://docs.temporal.io/production-deployment/data-encryption#codec-server-setup"
}
],
"solutions": [
{
"lang": "en",
"supportingMedia": [
{
"base64": false,
"type": "text/html",
"value": "\u003cp\u003eThe fix is expected in version 0.2.3. Upgrade to version 0.2.3 or later when available.\u003c/p\u003e"
}
],
"value": "The fix is expected in version 0.2.3. Upgrade to version 0.2.3 or later when available."
}
],
"source": {
"discovery": "EXTERNAL"
},
"title": "s2s-proxy accepts untrusted client certificates",
"workarounds": [
{
"lang": "en",
"supportingMedia": [
{
"base64": false,
"type": "text/html",
"value": "\u003cp\u003eRestrict the listener to known peer addresses or a private network, or use a TLS terminator that verifies client certificates against the intended CA. These controls reduce exposure but do not fix the proxy defect.\u003c/p\u003e"
}
],
"value": "Restrict the listener to known peer addresses or a private network, or use a TLS terminator that verifies client certificates against the intended CA. These controls reduce exposure but do not fix the proxy defect."
}
]
}
},
"cveMetadata": {
"assignerOrgId": "61241ed8-fa44-4f23-92db-b8c443751968",
"assignerShortName": "Temporal",
"cveId": "CVE-2026-96770",
"datePublished": "2026-09-23T18:58:46.233Z",
"dateReserved": "2026-09-23T16:06:36.077Z",
"dateUpdated": "2026-09-23T19:36:12.488Z",
"state": "PUBLISHED"
},
"dataType": "CVE_RECORD",
"dataVersion": "5.2"
}
}
}
Loading…
Loading…
Experimental. This forecast is provided for visualization only and may change without notice. Do not use it for operational decisions.
Forecast uses a logistic model when the trend is rising, or an exponential decay model when the trend is falling. Fitted via linearized least squares.
Sightings
| Author | Source | Type | Date | Other |
|---|
Nomenclature
- Seen: The vulnerability was mentioned, discussed, or observed by the user.
- Confirmed: The vulnerability has been validated from an analyst's perspective.
- Published Proof of Concept: A public proof of concept is available for this vulnerability.
- Exploited: The vulnerability was observed as exploited by the user who reported the sighting.
- Patched: The vulnerability was observed as successfully patched by the user who reported the sighting.
- Not exploited: The vulnerability was not observed as exploited by the user who reported the sighting.
- Not confirmed: The user expressed doubt about the validity of the vulnerability.
- Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.
Loading…
Loading…
The MITRE ATT&CK techniques below are AI-generated suggestions, inferred from the description of the
vulnerability by the CIRCL/vulnerability-attack-technique-classification-roberta-base
model, served locally by ML-Gateway.
They have not been verified by an analyst and are provided for guidance only.
The approach is described in our paper Mapping CVEs to MITRE ATT&CK Techniques: A Curated Gold-Set Classifier and the Limits of LLM-Assisted Label Expansion.
Browse all ATT&CK techniques and the vulnerabilities related to each.
The approach is described in our paper Mapping CVEs to MITRE ATT&CK Techniques: A Curated Gold-Set Classifier and the Limits of LLM-Assisted Label Expansion.
Browse all ATT&CK techniques and the vulnerabilities related to each.
Loading…
Related by attack behaviour
Vulnerabilities whose description is nearest to this one in the vector space of the CIRCL/vulnerability-attack-technique-biencoder model. This is a similarity search over the bi-encoder space (plain cosine), not a classification, and it has no measured accuracy.
Loading…