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GHSA-GXJC-74V5-3VX3

Vulnerability from github – Published: 2026-09-18 17:14 – Updated: 2026-09-18 17:14
VLAI
Summary
Capsule: Malformed ForbiddenAnnotations.Regex can bypass Tenant validation and trigger namespace admission panic
Details

Summary

A validation bug in internal/webhook/tenant/validation/forbidden_annotations_regex.go allows an invalid ForbiddenAnnotations.Regex value to bypass Tenant admission on update. The webhook compiles ForbiddenLabels.Regex for both labels and annotations, so a malformed annotations regex can be persisted. Once stored, namespace admission later evaluates the bad regex through pkg/api/forbidden_list.go, where regexp.MustCompile can panic and cause admission failure.

Details

In internal/webhook/tenant/validation/forbidden_annotations_regex.go, OnUpdate validates the new Tenant object, but the loop compiles tnt.Spec.NamespaceOptions.ForbiddenLabels.Regex for both labels and annotations. That means an invalid ForbiddenAnnotations.Regex is never validated if ForbiddenLabels.Regex is valid.

Relevant paths: - internal/webhook/tenant/validation/forbidden_annotations_regex.go - internal/webhook/namespace/validation/user_metadata.go - pkg/api/forbidden_list.go

Namespace admission later calls api.ValidateForbidden(...), and ForbiddenListSpec.RegexMatch() uses regexp.MustCompile(in.Regex). If the malformed regex is present in the Tenant spec, any namespace request that reaches this check can panic or fail hard, causing denial of service for namespace operations in the affected tenant.

PoC

  1. Update a Tenant so that:
  2. spec.namespaceOptions.forbiddenLabels.regex is valid
  3. spec.namespaceOptions.forbiddenAnnotations.regex is malformed, for example: [invalid-regex(
  4. The Tenant update is accepted because the webhook compiles the labels regex for both fields.
  5. Create or update a Namespace that triggers forbidden metadata validation.
  6. The namespace admission path reaches regexp.MustCompile(...) and panics.
package main

import (
    "fmt"
    "regexp"
)

type ForbiddenListSpec struct {
    Regex string
}

type NamespaceOptions struct {
    ForbiddenLabels      ForbiddenListSpec
    ForbiddenAnnotations ForbiddenListSpec
}

type Tenant struct {
    NamespaceOptions *NamespaceOptions
}

func validateTenantUpdate(tnt *Tenant) error {
    if tnt.NamespaceOptions == nil {
        return nil
    }

    annotationsToCheck := map[string]string{
        "labels":      tnt.NamespaceOptions.ForbiddenLabels.Regex,
        "annotations": tnt.NamespaceOptions.ForbiddenAnnotations.Regex,
    }

    for scope, annotation := range annotationsToCheck {
        if _, err := regexp.Compile(tnt.NamespaceOptions.ForbiddenLabels.Regex); err != nil {
            return fmt.Errorf("deny update: unable to compile %s regex for forbidden %s", annotation, scope)
        }
    }

    return nil
}

func validateForbidden(metadata map[string]string, forbidden ForbiddenListSpec) error {
    for key := range metadata {
        if forbidden.Regex != "" {
            if regexp.MustCompile(forbidden.Regex).MatchString(key) {
                return fmt.Errorf("forbidden key matched: %s", key)
            }
        }
    }

    return nil
}

func main() {
    oldTenant := &Tenant{
        NamespaceOptions: &NamespaceOptions{
            ForbiddenLabels:      ForbiddenListSpec{Regex: `^[a-z0-9-]+$`},
            ForbiddenAnnotations: ForbiddenListSpec{Regex: `^[a-z0-9-]+$`},
        },
    }

    newTenant := &Tenant{
        NamespaceOptions: &NamespaceOptions{
            ForbiddenLabels:      ForbiddenListSpec{Regex: `^[a-z0-9-]+$`},
            ForbiddenAnnotations: ForbiddenListSpec{Regex: `[invalid-regex(`},
        },
    }

    fmt.Println("=== Update step ===")
    if err := validateTenantUpdate(newTenant); err != nil {
        fmt.Printf("unexpected deny: %v\n", err)
    } else {
        fmt.Println("allowed: malformed ForbiddenAnnotations.Regex bypassed validation")
    }

    fmt.Println()
    fmt.Println("=== Namespace step ===")
    _ = oldTenant

    defer func() {
        if r := recover(); r != nil {
            fmt.Printf("panic reproduced from ValidateForbidden: %v\n", r)
        }
    }()

    _ = validateForbidden(map[string]string{"example": "value"}, ForbiddenListSpec{Regex: `[invalid-regex(`})
    fmt.Println("no panic, unexpected")
}

Expected output:

=== Update step ===
allowed: malformed ForbiddenAnnotations.Regex bypassed validation

=== Namespace step ===
panic reproduced from ValidateForbidden: regexp: Compile(`[invalid-regex(`): error parsing regexp: missing closing ]: `[invalid-regex(`

Impact

An attacker who can update the Tenant configuration can persist a malformed ForbiddenAnnotations.Regex and cause namespace admission failures for the affected tenant. This can result in a tenant-scoped denial of service.

Severity
4.9 (Medium)
CVSS:3.1/AV:N/AC:L/PR:H/UI:N/S:U/C:N/I:N/A:H
Show details on source website
To clipboard 

{
  "affected": [
    {
      "package": {
        "ecosystem": "Go",
        "name": "github.com/projectcapsule/capsule"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0.13.0"
            },
            {
              "fixed": "0.13.7"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    }
  ],
  "aliases": [
    "CVE-2026-61794"
  ],
  "database_specific": {
    "cwe_ids": [
      "CWE-20"
    ],
    "github_reviewed": true,
    "github_reviewed_at": "2026-09-18T17:14:26Z",
    "nvd_published_at": null,
    "severity": "MODERATE"
  },
  "details": "### Summary\nA validation bug in `internal/webhook/tenant/validation/forbidden_annotations_regex.go` allows an invalid `ForbiddenAnnotations.Regex` value to bypass Tenant admission on update. The webhook compiles `ForbiddenLabels.Regex` for both labels and annotations, so a malformed annotations regex can be persisted. Once stored, namespace admission later evaluates the bad regex through `pkg/api/forbidden_list.go`, where `regexp.MustCompile` can panic and cause admission failure.\n\n### Details\nIn `internal/webhook/tenant/validation/forbidden_annotations_regex.go`, `OnUpdate` validates the new Tenant object, but the loop compiles `tnt.Spec.NamespaceOptions.ForbiddenLabels.Regex` for both `labels` and `annotations`. That means an invalid `ForbiddenAnnotations.Regex` is never validated if `ForbiddenLabels.Regex` is valid.\n\nRelevant paths:\n- `internal/webhook/tenant/validation/forbidden_annotations_regex.go`\n- `internal/webhook/namespace/validation/user_metadata.go`\n- `pkg/api/forbidden_list.go`\n\nNamespace admission later calls `api.ValidateForbidden(...)`, and `ForbiddenListSpec.RegexMatch()` uses `regexp.MustCompile(in.Regex)`. If the malformed regex is present in the Tenant spec, any namespace request that reaches this check can panic or fail hard, causing denial of service for namespace operations in the affected tenant.\n\n\n### PoC\n1. Update a Tenant so that:\n   - `spec.namespaceOptions.forbiddenLabels.regex` is valid\n   - `spec.namespaceOptions.forbiddenAnnotations.regex` is malformed, for example: `[invalid-regex(`\n2. The Tenant update is accepted because the webhook compiles the labels regex for both fields.\n3. Create or update a Namespace that triggers forbidden metadata validation.\n4. The namespace admission path reaches `regexp.MustCompile(...)` and panics.\n\n```\npackage main\n\nimport (\n\t\"fmt\"\n\t\"regexp\"\n)\n\ntype ForbiddenListSpec struct {\n\tRegex string\n}\n\ntype NamespaceOptions struct {\n\tForbiddenLabels      ForbiddenListSpec\n\tForbiddenAnnotations ForbiddenListSpec\n}\n\ntype Tenant struct {\n\tNamespaceOptions *NamespaceOptions\n}\n\nfunc validateTenantUpdate(tnt *Tenant) error {\n\tif tnt.NamespaceOptions == nil {\n\t\treturn nil\n\t}\n\n\tannotationsToCheck := map[string]string{\n\t\t\"labels\":      tnt.NamespaceOptions.ForbiddenLabels.Regex,\n\t\t\"annotations\": tnt.NamespaceOptions.ForbiddenAnnotations.Regex,\n\t}\n\n\tfor scope, annotation := range annotationsToCheck {\n\t\tif _, err := regexp.Compile(tnt.NamespaceOptions.ForbiddenLabels.Regex); err != nil {\n\t\t\treturn fmt.Errorf(\"deny update: unable to compile %s regex for forbidden %s\", annotation, scope)\n\t\t}\n\t}\n\n\treturn nil\n}\n\nfunc validateForbidden(metadata map[string]string, forbidden ForbiddenListSpec) error {\n\tfor key := range metadata {\n\t\tif forbidden.Regex != \"\" {\n\t\t\tif regexp.MustCompile(forbidden.Regex).MatchString(key) {\n\t\t\t\treturn fmt.Errorf(\"forbidden key matched: %s\", key)\n\t\t\t}\n\t\t}\n\t}\n\n\treturn nil\n}\n\nfunc main() {\n\toldTenant := \u0026Tenant{\n\t\tNamespaceOptions: \u0026NamespaceOptions{\n\t\t\tForbiddenLabels:      ForbiddenListSpec{Regex: `^[a-z0-9-]+$`},\n\t\t\tForbiddenAnnotations: ForbiddenListSpec{Regex: `^[a-z0-9-]+$`},\n\t\t},\n\t}\n\n\tnewTenant := \u0026Tenant{\n\t\tNamespaceOptions: \u0026NamespaceOptions{\n\t\t\tForbiddenLabels:      ForbiddenListSpec{Regex: `^[a-z0-9-]+$`},\n\t\t\tForbiddenAnnotations: ForbiddenListSpec{Regex: `[invalid-regex(`},\n\t\t},\n\t}\n\n\tfmt.Println(\"=== Update step ===\")\n\tif err := validateTenantUpdate(newTenant); err != nil {\n\t\tfmt.Printf(\"unexpected deny: %v\\n\", err)\n\t} else {\n\t\tfmt.Println(\"allowed: malformed ForbiddenAnnotations.Regex bypassed validation\")\n\t}\n\n\tfmt.Println()\n\tfmt.Println(\"=== Namespace step ===\")\n\t_ = oldTenant\n\n\tdefer func() {\n\t\tif r := recover(); r != nil {\n\t\t\tfmt.Printf(\"panic reproduced from ValidateForbidden: %v\\n\", r)\n\t\t}\n\t}()\n\n\t_ = validateForbidden(map[string]string{\"example\": \"value\"}, ForbiddenListSpec{Regex: `[invalid-regex(`})\n\tfmt.Println(\"no panic, unexpected\")\n}\n```\nExpected output:\n\n```text\n=== Update step ===\nallowed: malformed ForbiddenAnnotations.Regex bypassed validation\n\n=== Namespace step ===\npanic reproduced from ValidateForbidden: regexp: Compile(`[invalid-regex(`): error parsing regexp: missing closing ]: `[invalid-regex(`\n```\n\n\n\n### Impact\nAn attacker who can update the Tenant configuration can persist a malformed `ForbiddenAnnotations.Regex` and cause namespace admission failures for the affected tenant. This can result in a tenant-scoped denial of service.",
  "id": "GHSA-gxjc-74v5-3vx3",
  "modified": "2026-09-18T17:14:26Z",
  "published": "2026-09-18T17:14:26Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://github.com/projectcapsule/capsule/security/advisories/GHSA-gxjc-74v5-3vx3"
    },
    {
      "type": "WEB",
      "url": "https://github.com/projectcapsule/capsule/pull/1983"
    },
    {
      "type": "WEB",
      "url": "https://github.com/projectcapsule/capsule/commit/8d89d6865df6f41c7faa22fc9e807a57b01bfd0e"
    },
    {
      "type": "PACKAGE",
      "url": "https://github.com/projectcapsule/capsule"
    },
    {
      "type": "WEB",
      "url": "https://github.com/projectcapsule/capsule/releases/tag/v0.13.7"
    }
  ],
  "schema_version": "1.4.0",
  "severity": [
    {
      "score": "CVSS:3.1/AV:N/AC:L/PR:H/UI:N/S:U/C:N/I:N/A:H",
      "type": "CVSS_V3"
    }
  ],
  "summary": "Capsule: Malformed ForbiddenAnnotations.Regex can bypass Tenant validation and trigger namespace admission panic"
}



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