Vulnerability-Lookup

CVE-2026-33397 (GCVE-0-2026-33397)

Vulnerability from cvelistv5 – Published: 2026-03-26 13:46 – Updated: 2026-03-30 14:56

Title

Angular SSR Vulnerable to Protocol-Relative URL Injection via Single Backslash Bypass

Summary

The Angular SSR is a server-rise rendering tool for Angular applications. Versions on the 22.x branch prior to 22.0.0-next.2, the 21.x branch prior to 21.2.3, and the 20.x branch prior to 20.3.21 have an Open Redirect vulnerability in `@angular/ssr` due to an incomplete fix for CVE-2026-27738. While the original fix successfully blocked multiple leading slashes (e.g., `///`), the internal validation logic fails to account for a single backslash (`\`) bypass. When an Angular SSR application is deployed behind a proxy that passes the `X-Forwarded-Prefix` header, an attacker provides a value starting with a single backslash, the internal validation failed to flag the single backslash as invalid, the application prepends a leading forward slash, resulting in a `Location` header containing the URL, and modern browsers interpret the `/\` sequence as `//`, treating it as a protocol-relative URL and redirecting the user to the attacker-controlled domain. Furthermore, the response lacks the `Vary: X-Forwarded-Prefix` header, allowing the malicious redirect to be stored in intermediate caches (Web Cache Poisoning). Versions 22.0.0-next.2, 21.2.3, and 20.3.21 contain a patch. Until the patch is applied, developers should sanitize the `X-Forwarded-Prefix` header in their `server.ts` before the Angular engine processes the request.

Severity

6.9 (Medium)


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

SSVC

Exploitation: none Automatable: yes Technical Impact: partial

CISA Coordinator · CISA-ADP (v2.0.3)

Decision recorded 2026-03-30 13:54 UTC

CWE

CWE-601 - URL Redirection to Untrusted Site ('Open Redirect')

Assigner

GitHub_M mitre root

References

3 references

URL	Tags
https://github.com/angular/angular-cli/security/a…	x_refsource_CONFIRM
https://github.com/angular/angular-cli/pull/32771	x_refsource_MISC
https://github.com/advisories/GHSA-xh43-g2fq-wjrj	x_refsource_MISC

Impacted products

1 product

Vendor	Product	Version
angular	angular-cli	Affected: >= 22.0.0-next.0, < 22.0.0-next.2 Affected: >= 21.0.0-next.0, < 21.2.3 Affected: >= 20.0.0-next.0, < 20.3.21

Show details on NVD website

JSON

To clipboard

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EUVD-2026-55317

European Vulnerability Database identifier assigned by ENISA

Reserved

2026-10-03 10:48

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": "2026-10-03T10:48:35.910338+00:00",
  "id": "EUVD-2026-55317"
}

FKIE_CVE-2026-33397

Vulnerability from fkie_nvd - Published: 2026-03-26 15:16 - Updated: 2026-06-17 10:37

Severity

6.1 (Medium) - CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N

Summary

References

URL	Tags
security-advisories@github.com	https://github.com/advisories/GHSA-xh43-g2fq-wjrj	Not Applicable
security-advisories@github.com	https://github.com/angular/angular-cli/pull/32771	Issue Tracking, Patch
security-advisories@github.com	https://github.com/angular/angular-cli/security/advisories/GHSA-vfx2-hv2g-xj5f	Vendor Advisory

Impacted products

Vendor	Product	Version
angular	angular_cli	*
angular	angular_cli	*
angular	angular_cli	22.0.0
angular	angular_cli	22.0.0

JSON

To clipboard

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  "lastModified": "2026-06-17T10:37:25.300",
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  },
  "published": "2026-03-26T15:16:38.533",
  "references": [
    {
      "source": "security-advisories@github.com",
      "tags": [
        "Not Applicable"
      ],
      "url": "https://github.com/advisories/GHSA-xh43-g2fq-wjrj"
    },
    {
      "source": "security-advisories@github.com",
      "tags": [
        "Issue Tracking",
        "Patch"
      ],
      "url": "https://github.com/angular/angular-cli/pull/32771"
    },
    {
      "source": "security-advisories@github.com",
      "tags": [
        "Vendor Advisory"
      ],
      "url": "https://github.com/angular/angular-cli/security/advisories/GHSA-vfx2-hv2g-xj5f"
    }
  ],
  "sourceIdentifier": "security-advisories@github.com",
  "vulnStatus": "Analyzed",
  "weaknesses": [
    {
      "description": [
        {
          "lang": "en",
          "value": "CWE-601"
        }
      ],
      "source": "security-advisories@github.com",
      "type": "Secondary"
    }
  ]
}

GHSA-VFX2-HV2G-XJ5F

Vulnerability from github – Published: 2026-03-19 21:22 – Updated: 2026-05-06 20:32

Summary

Protocol-Relative URL Injection via Single Backslash Bypass in Angular SSR

Details

An Open Redirect vulnerability exists in @angular/ssr due to an incomplete fix for CVE-2026-27738. While the original fix successfully blocked multiple leading slashes (e.g., ///), the internal validation logic fails to account for a single backslash (\) bypass.

When an Angular SSR application is deployed behind a proxy that passes the X-Forwarded-Prefix header:

An attacker provides a value starting with a single backslash (e.g., \evil.com).
The internal validation failed to flag the single backslash as invalid.
The application prepends a leading forward slash, resulting in a Location header containing /\evil.com.
Modern browsers interpret the /\ sequence as //, treating it as a protocol-relative URL and redirecting the user to the attacker-controlled domain.

Furthermore, the response lacks the Vary: X-Forwarded-Prefix header, allowing the malicious redirect to be stored in intermediate caches (Web Cache Poisoning).

Impact

This vulnerability allows attackers to conduct large-scale phishing and SEO hijacking:

Scale: A single request can poison a high-traffic route, impacting all users until the cache expires.
SEO Poisoning: Search engine crawlers may follow and index these malicious redirects, causing the legitimate site to be delisted or associated with malicious domains.
Trust: Because the initial URL belongs to the trusted domain, users and security tools are less likely to flag the redirect as malicious.

Patches

22.0.0-next.2
21.2.3
20.3.21

Workarounds

Until the patch is applied, developers should sanitize the X-Forwarded-Prefix header in their server.ts before the Angular engine processes the request:

app.use((req, res, next) => {
  const prefix = req.headers['x-forwarded-prefix'];
  if (typeof prefix === 'string') {
    // Sanitize by removing all leading forward and backward slashes
    req.headers['x-forwarded-prefix'] = prefix.trim().replace(/^[/\\]+/, '/');
  }
  next();
});

References

Fix: https://github.com/angular/angular-cli/pull/32771
Original CVE: CVE-2026-27738

Severity

6.1 (Medium)


                  
                    CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N

6.9 (Medium)


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

Show details on source website

JSON

To clipboard

{
  "affected": [
    {
      "package": {
        "ecosystem": "npm",
        "name": "@angular/ssr"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "22.0.0-next.0"
            },
            {
              "fixed": "22.0.0-next.2"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    },
    {
      "package": {
        "ecosystem": "npm",
        "name": "@angular/ssr"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "21.0.0-next.0"
            },
            {
              "fixed": "21.2.3"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    },
    {
      "package": {
        "ecosystem": "npm",
        "name": "@angular/ssr"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "20.0.0-next.0"
            },
            {
              "fixed": "20.3.21"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    }
  ],
  "aliases": [
    "CVE-2026-33397"
  ],
  "database_specific": {
    "cwe_ids": [
      "CWE-601"
    ],
    "github_reviewed": true,
    "github_reviewed_at": "2026-03-19T21:22:52Z",
    "nvd_published_at": "2026-03-26T15:16:38Z",
    "severity": "MODERATE"
  },
  "details": "An Open Redirect vulnerability exists in `@angular/ssr` due to an incomplete fix for CVE-2026-27738. While the original fix successfully blocked multiple leading slashes (e.g., `///`), the internal validation logic fails to account for a single backslash (`\\`) bypass.\n\nWhen an Angular SSR application is deployed behind a proxy that passes the `X-Forwarded-Prefix` header:\n\n- An attacker provides a value starting with a single backslash (e.g., `\\evil.com`).\n- The internal validation failed to flag the single backslash as invalid.\n- The application prepends a leading forward slash, resulting in a `Location` header containing `/\\evil.com`.\n- Modern browsers interpret the `/\\` sequence as `//`, treating it as a protocol-relative URL and redirecting the user to the attacker-controlled domain.\n\nFurthermore, the response lacks the `Vary: X-Forwarded-Prefix` header, allowing the malicious redirect to be stored in intermediate caches (Web Cache Poisoning).\n\n### Impact\nThis vulnerability allows attackers to conduct large-scale phishing and SEO hijacking:\n\n- **Scale**: A single request can poison a high-traffic route, impacting all users until the cache expires.\n- **SEO Poisoning**: Search engine crawlers may follow and index these malicious redirects, causing the legitimate site to be delisted or associated with malicious domains.\n- **Trust**: Because the initial URL belongs to the trusted domain, users and security tools are less likely to flag the redirect as malicious.\n\n### Patches\n\n- 22.0.0-next.2\n- 21.2.3\n- 20.3.21\n\n### Workarounds\nUntil the patch is applied, developers should sanitize the `X-Forwarded-Prefix` header in their `server.ts` before the Angular engine processes the request:\n\n```ts\napp.use((req, res, next) =\u003e {\n  const prefix = req.headers[\u0027x-forwarded-prefix\u0027];\n  if (typeof prefix === \u0027string\u0027) {\n    // Sanitize by removing all leading forward and backward slashes\n    req.headers[\u0027x-forwarded-prefix\u0027] = prefix.trim().replace(/^[/\\\\]+/, \u0027/\u0027);\n  }\n  next();\n});\n```\n\n\n### References\n\n- Fix: https://github.com/angular/angular-cli/pull/32771\n- Original CVE: CVE-2026-27738",
  "id": "GHSA-vfx2-hv2g-xj5f",
  "modified": "2026-05-06T20:32:54Z",
  "published": "2026-03-19T21:22:52Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://github.com/angular/angular-cli/security/advisories/GHSA-vfx2-hv2g-xj5f"
    },
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-33397"
    },
    {
      "type": "WEB",
      "url": "https://github.com/angular/angular-cli/pull/32771"
    },
    {
      "type": "ADVISORY",
      "url": "https://github.com/advisories/GHSA-xh43-g2fq-wjrj"
    },
    {
      "type": "PACKAGE",
      "url": "https://github.com/angular/angular-cli"
    }
  ],
  "schema_version": "1.4.0",
  "severity": [
    {
      "score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N",
      "type": "CVSS_V3"
    },
    {
      "score": "CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:N/SC:L/SI:L/SA:N",
      "type": "CVSS_V4"
    }
  ],
  "summary": "Protocol-Relative URL Injection via Single Backslash Bypass in Angular SSR"
}

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.

Detection rules are retrieved from Rulezet.

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.

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.

Action not permitted

CVE-2026-33397 (GCVE-0-2026-33397)

EUVD-2026-55317

FKIE_CVE-2026-33397

GHSA-VFX2-HV2G-XJ5F

Impact

Patches

Workarounds

References

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