Vulnerability-Lookup

CVE-2026-42273 (GCVE-0-2026-42273)

Vulnerability from cvelistv5 – Published: 2026-05-08 03:42 – Updated: 2026-05-08 10:40

Title

Heimdall: Case-sensitive host matching may lead to policy bypass

Summary

Heimdall is a cloud native Identity Aware Proxy and Access Control Decision service. Prior to version 0.17.14, Heimdall performs host matching in a case-sensitive manner, while HTTP hostnames are case-insensitive. This discrepancy can result in heimdall failing to match a rule for a request host that differs only in letter casing, potentially causing the request to be classified differently than intended. This issue has been patched in version 0.17.14.

Severity

7.8 (High)


                        
                          CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:N/SC:H/SI:H/SA:N

SSVC

Exploitation: none Automatable: yes Technical Impact: partial

CISA Coordinator · CISA-ADP (v2.0.3)

Decision recorded 2026-05-08 10:40 UTC

CWE

CWE-436 - Interpretation Conflict
CWE-178 - Improper Handling of Case Sensitivity

Assigner

GitHub_M mitre root Scorecard

References

4 references

URL	Tags
https://github.com/dadrus/heimdall/security/advis…	x_refsource_CONFIRM
https://github.com/dadrus/heimdall/pull/3208	x_refsource_MISC
https://github.com/dadrus/heimdall/commit/3d05e56…	x_refsource_MISC
https://github.com/dadrus/heimdall/releases/tag/v…	x_refsource_MISC

Impacted products

1 product

Vendor	Product	Version
dadrus	heimdall	Affected: < 0.17.14

Show details on NVD website

JSON

To clipboard

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}

EUVD-2026-309105

European Vulnerability Database identifier assigned by ENISA

Reserved

2026-10-02 07:08

Assigner

ENISA

Alias of

a CVE record, shown under related vulnerabilities. This identifier carries no description, severity or references of its own: they belong to that CVE.

JSON

To clipboard

{
  "assigner": "ENISA",
  "date_reserved": "2026-10-02T07:08:55.024739+00:00",
  "id": "EUVD-2026-309105"
}

FKIE_CVE-2026-42273

Vulnerability from fkie_nvd - Published: 2026-05-08 04:16 - Updated: 2026-06-17 10:47

Severity

7.8 (High) - CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:N/SC:H/SI:H/SA:N

Summary

References

	URL	Tags
	security-advisories@github.com	https://github.com/dadrus/heimdall/commit/3d05e56a9e7ef0355f17482b4322054af4e85943
	security-advisories@github.com	https://github.com/dadrus/heimdall/pull/3208
	security-advisories@github.com	https://github.com/dadrus/heimdall/releases/tag/v0.17.14
	security-advisories@github.com	https://github.com/dadrus/heimdall/security/advisories/GHSA-72h4-mxfc-jx37

Impacted products

	Vendor	Product	Version

JSON

To clipboard

{
  "affected": [
    {
      "affectedData": [
        {
          "product": "heimdall",
          "vendor": "dadrus",
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            {
              "status": "affected",
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    }
  ],
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  "lastModified": "2026-06-17T10:47:36.787",
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          "attackVector": "NETWORK",
          "availabilityRequirement": "NOT_DEFINED",
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          "modifiedAttackVector": "NOT_DEFINED",
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GHSA-72H4-MXFC-JX37

Vulnerability from github – Published: 2026-04-25 23:30 – Updated: 2026-05-12 13:28

Summary

Heimdall: Case-sensitive host matching may lead to policy bypass

Details

Summary

Heimdall performs host matching in a case-sensitive manner, while HTTP hostnames are case-insensitive. This discrepancy can result in heimdall failing to match a rule for a request host that differs only in letter casing, potentially causing the request to be classified differently than intended.

Note: The issue can only lead to unintended access if heimdall is configured with an "allow all" default rule. Since v0.16.0, heimdall enforces secure defaults and refuses to start with such a configuration unless this enforcement is explicitly disabled, e.g. via --insecure-skip-secure-default-rule-enforcement or the broader --insecure flag.

Details

This vulnerability can potentially be exploited by an adversary if rule matching relies on the request host.

For example, consider the following rule:

id: rule-1
match:
  hosts:
    - type: exact
      value: admin.example.com
execute: # configured to require authentication and authorization
  # ...

If an adversary now sends a request with the Host header set to Admin.Example.Com, rule-1 will not be matched, and the following will happen instead:

If no default rule is configured, the request will result in an error (404 Not Found)
If a default rule is configured, it will be executed. If the default rule is configured in an overly permissive way (e.g. allowing anonymous access), this results in a policy bypass.

Impact

Bypass of access control policies enforced by heimdall may lead to the following consequences:

Access to or modification of data that should be restricted
Invocation of functionality that is expected to require authentication or authorization
In certain configurations, escalation of privileges depending on the exposed functionality

Workarounds

Normalize request hosts to lowercase in the layers in front of heimdall.
Do not configure a permissive default rule. Respectively, do not make use of the --insecure or the --insecure-skip-secure-default-rule-enforcement flags.
When using regex type for host matching, expressions shall be defined in a case-insensitive manner (e.g. (?i)^admin\.example\.com$)
Include the ID of the rule expected to be executed in the JWT issued by heimdall and check that value in the consuming project's service.

Severity

7.8 (High)


                  
                    CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:N/SC:H/SI:H/SA:N

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{
  "affected": [
    {
      "package": {
        "ecosystem": "Go",
        "name": "github.com/dadrus/heimdall"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            },
            {
              "fixed": "0.17.14"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    }
  ],
  "aliases": [
    "CVE-2026-42273"
  ],
  "database_specific": {
    "cwe_ids": [
      "CWE-178",
      "CWE-436"
    ],
    "github_reviewed": true,
    "github_reviewed_at": "2026-04-25T23:30:18Z",
    "nvd_published_at": "2026-05-08T04:16:22Z",
    "severity": "HIGH"
  },
  "details": "### Summary\n\nHeimdall performs host matching in a case-sensitive manner, while HTTP hostnames are case-insensitive. This discrepancy can result in heimdall failing to match a rule for a request host that differs only in letter casing, potentially causing the request to be classified differently than intended.\n\n**Note:** The issue can only lead to unintended access if heimdall is configured with an \"allow all\" default rule. Since v0.16.0, heimdall enforces secure defaults and refuses to start with such a configuration unless this enforcement is explicitly disabled, e.g. via `--insecure-skip-secure-default-rule-enforcement` or the broader `--insecure` flag.\n\n### Details\n\nThis vulnerability can potentially be exploited by an adversary if rule matching relies on the request host.\n\nFor example, consider the following rule:\n\n```yaml\nid: rule-1\nmatch:\n  hosts:\n    - type: exact\n      value: admin.example.com\nexecute: # configured to require authentication and authorization\n  # ...\n```\n\nIf an adversary now sends a request with the `Host` header set to `Admin.Example.Com`, rule-1 will not be matched, and the following will happen instead:\n\n* If no default rule is configured, the request will result in an error (`404 Not Found`)\n* If a default rule is configured, it will be executed. If the default rule is configured in an overly permissive way (e.g. allowing anonymous access), this results in a policy bypass.\n\n### Impact\n\nBypass of access control policies enforced by heimdall may lead to the following consequences:\n\n* Access to or modification of data that should be restricted\n* Invocation of functionality that is expected to require authentication or authorization\n* In certain configurations, escalation of privileges depending on the exposed functionality\n\n### Workarounds\n\n* Normalize request hosts to lowercase in the layers in front of heimdall.\n* Do not configure a permissive default rule. Respectively, do not make use of the `--insecure` or the `--insecure-skip-secure-default-rule-enforcement` flags.\n* When using `regex` type for host matching, expressions shall be defined in a case-insensitive manner (e.g. `(?i)^admin\\.example\\.com$`)\n* Include the ID of the rule expected to be executed in the JWT issued by heimdall and check that value in the consuming project\u0027s service.",
  "id": "GHSA-72h4-mxfc-jx37",
  "modified": "2026-05-12T13:28:54Z",
  "published": "2026-04-25T23:30:18Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://github.com/dadrus/heimdall/security/advisories/GHSA-72h4-mxfc-jx37"
    },
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-42273"
    },
    {
      "type": "WEB",
      "url": "https://github.com/dadrus/heimdall/pull/3208"
    },
    {
      "type": "WEB",
      "url": "https://github.com/dadrus/heimdall/commit/3d05e56a9e7ef0355f17482b4322054af4e85943"
    },
    {
      "type": "PACKAGE",
      "url": "https://github.com/dadrus/heimdall"
    },
    {
      "type": "WEB",
      "url": "https://github.com/dadrus/heimdall/releases/tag/v0.17.14"
    }
  ],
  "schema_version": "1.4.0",
  "severity": [
    {
      "score": "CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:N/SC:H/SI:H/SA:N",
      "type": "CVSS_V4"
    }
  ],
  "summary": "Heimdall: Case-sensitive host matching may lead to policy bypass"
}

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.

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.

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Action not permitted

CVE-2026-42273 (GCVE-0-2026-42273)

EUVD-2026-309105

FKIE_CVE-2026-42273

GHSA-72H4-MXFC-JX37

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