# CVE-2026-61795: Capsule: hostnameRegexHandler.OnUpdate validates stale (old) Tenant regex, allowing invalid AllowedHostnames regex to bypass webhook validation > CVE-2026-61795 (GitHub advisory GHSA-f94q-w3w8-cj67) is a medium-severity vulnerability with a CVSS 3.1 base score of 6.8, classed as Incorrect Comparison (CWE-697), in github.com/projectcapsule/capsule (Go). Affected versions: >= 0.13.0, < 0.13.7. It is fixed in 0.13.7. Canonical page: https://cveminer.com/vulnerabilities/CVE-2026-61795 | Field | Value | | --- | --- | | CVE | CVE-2026-61795 | | GHSA | GHSA-f94q-w3w8-cj67 | | Severity | Medium | | CVSS 3.1 | 6.8 `CVSS:3.1/AV:N/AC:L/PR:H/UI:N/S:C/C:N/I:N/A:H` (GitHub Advisory Database) | | CWE | CWE-697 Incorrect Comparison | | EPSS | 0.32% (higher than 26% of CVEs) | | CISA KEV | Not listed | | Published | 18 Sept 2026 | | Modified | 18 Sept 2026 | ## Description A parameter order bug in `internal/webhook/tenant/validation/hostname_regex.go` causes the `hostnameRegexHandler.OnUpdate` webhook to validate the **old** Tenant object's `AllowedHostnames.Regex` instead of the **new** one being submitted. This allows an invalid (malformed) regex to bypass admission validation and be persisted to etcd, causing a Denial of Service for all Ingress operations within the affected tenant. ##### Details The `TypedHandler[T]` interface defines `OnUpdate` as: ```go // handlers.go OnUpdate(c client.Client, reader client.Reader, obj T, old T, decoder admission.Decoder, recorder events.EventRecorder) Func // ^^^ NEW ^^^ OLD ``` The dispatcher in `handler.go:93` calls: ```go hndl.OnUpdate(c, reader, tnt, old, decoder, recorder) // ^^^ NEW ^^^ OLD ``` However, `hostnameRegexHandler.OnUpdate` in `hostname_regex.go` declares its parameters in **reversed order**: ```go // hostname_regex.go (BUGGY) func (h *hostnameRegexHandler) OnUpdate( _ client.Client, _ client.Reader, old *capsulev1beta2.Tenant, // ← receives NEW tenant (mislabeled as old) tnt *capsulev1beta2.Tenant, // ← receives OLD tenant (mislabeled as tnt) ... ) handlers.Func { return func(...) *admission.Response { if err := h.validate(tnt, req); err != nil { // ← validates OLD, not NEW return err } return nil } } ``` All 11 other handlers in the same package declare `(tnt, old)` correctly. `hostname_regex.go` is the only one with the swap. As a result, when a Cluster Admin updates `Tenant.Spec.IngressOptions.AllowedHostnames.Regex` to a malformed value, the webhook compiles the **previous valid regex** and returns `Allow`. The malformed regex is then written to etcd. Subsequently, every Ingress `CREATE` or `UPDATE` in that tenant triggers `validate_hostnames.go:160`: ```go matched, _ = regexp.MatchString(allowedRegex, currentHostname) ``` `regexp.MatchString` with an invalid pattern returns `(false, error)`. The error is silently ignored, `matched` is `false`, and **every hostname is rejected** — blocking all Ingress operations in the tenant until the Tenant object is manually corrected by an admin. ##### PoC ``` //go:build ignore // Standalone reproducer for hostname_regex.go argument swap bug in Capsule // No external deps - shows the bug logic using only stdlib package main import ( "fmt" "regexp" ) // Simulating the Tenant spec structure type AllowedHostnames struct { Regex string } type IngressOptions struct { AllowedHostnames *AllowedHostnames } type TenantSpec struct { IngressOptions IngressOptions } type Tenant struct { Name string Spec TenantSpec } // ========================================================= // BUGGY implementation (hostname_regex.go as-is) // OnUpdate(_, _, old *Tenant, tnt *Tenant) → validates OLD // ========================================================= func hostnameValidate(tnt *Tenant) error { if tnt.Spec.IngressOptions.AllowedHostnames == nil { return nil } if len(tnt.Spec.IngressOptions.AllowedHostnames.Regex) == 0 { return nil } _, err := regexp.Compile(tnt.Spec.IngressOptions.AllowedHostnames.Regex) if err != nil { return fmt.Errorf("Deny: unable to compile allowedHostnames allowedRegex") } return nil } // Dispatcher calls: OnUpdate(c, reader, newTenant, oldTenant, ...) // Interface says: OnUpdate(c, reader, obj[NEW], old[OLD], ...) // // BUGGY handler receives: (old, tnt) meaning: // 3rd param (labeled "old") = actually NEW // 4th param (labeled "tnt") = actually OLD // Then calls h.validate(tnt) = validates the OLD tenant func buggyOnUpdate(newTenant, oldTenant *Tenant) error { // BUG: parameters are SWAPPED vs the interface contract old := newTenant // dispatcher's "new" arrives as "old" in this function tnt := oldTenant // dispatcher's "old" arrives as "tnt" in this function _ = old // unused in the real code too return hostnameValidate(tnt) // validates OLD, not NEW } // CORRECT implementation (what it should be) func correctOnUpdate(newTenant, oldTenant *Tenant) error { _ = oldTenant return hostnameValidate(newTenant) // validates NEW } // Simulate ingress hostname validation AFTER bad regex is stored func validateIngressHostname(tenant *Tenant, hostname string) bool { if tenant.Spec.IngressOptions.AllowedHostnames == nil { return true } allowedRegex := tenant.Spec.IngressOptions.AllowedHostnames.Regex if len(allowedRegex) == 0 { return true } // This is validate_hostnames.go:160 - error is IGNORED matched, _ := regexp.MatchString(allowedRegex, hostname) return matched } func main() { fmt.Println("=== Capsule Bug Reproducer: hostname_regex.go argument swap ===") fmt.Println() oldTenant := &Tenant{ Name: "demo-tenant", Spec: TenantSpec{ IngressOptions: IngressOptions{ AllowedHostnames: &AllowedHostnames{ Regex: `^[\w.-]+\.example\.com$`, // valid regex }, }, }, } // Attacker (cluster admin) sets an INVALID regex in the new spec newTenant := &Tenant{ Name: "demo-tenant", Spec: TenantSpec{ IngressOptions: IngressOptions{ AllowedHostnames: &AllowedHostnames{ Regex: `[invalid-regex(`, // INVALID regex }, }, }, } fmt.Printf("Old tenant regex: %q (valid)\n", oldTenant.Spec.IngressOptions.AllowedHostnames.Regex) fmt.Printf("New tenant regex: %q (INVALID)\n", newTenant.Spec.IngressOptions.AllowedHostnames.Regex) fmt.Println() // Step 1: Webhook runs OnUpdate fmt.Println("--- Step 1: Webhook OnUpdate ---") err := buggyOnUpdate(newTenant, oldTenant) if err != nil { fmt.Printf("[BUGGY] Webhook DENIES update: %v\n", err) } else { fmt.Println("[BUGGY] Webhook ALLOWS update (validates OLD regex) ← WRONG") } err = correctOnUpdate(newTenant, oldTenant) if err != nil { fmt.Printf("[CORRECT] Webhook DENIES update: %v ← EXPECTED\n", err) } else { fmt.Println("[CORRECT] Webhook ALLOWS update") } // Step 2: Invalid regex now stored in etcd - simulate ingress validation fmt.Println() fmt.Println("--- Step 2: Ingress creation after bad regex stored ---") storedTenant := newTenant // bad regex is now in etcd hostnames := []string{ "app.example.com", "api.example.com", "evil.attacker.com", } for _, h := range hostnames { allowed := validateIngressHostname(storedTenant, h) fmt.Printf(" Ingress hostname %q → allowed=%v", h, allowed) if !allowed { fmt.Print(" ← BLOCKED (DoS: invalid regex causes all hostnames to fail)") } fmt.Println() } fmt.Println() fmt.Println("=== Result ===") fmt.Println("Invalid regex bypasses webhook validation and gets stored.") fmt.Println("All subsequent Ingress create/update in this tenant are BLOCKED.") fmt.Println("CWE-697: Incorrect Comparison — wrong Tenant object is validated.") } ``` ```go // Simulates the buggy webhook behaviour oldTenant := &Tenant{AllowedRegex: `^[\w-]+\.example\.com$`} // valid newTenant := &Tenant{AllowedRegex: `[invalid-regex(`} // malformed // Buggy OnUpdate: validates oldTenant (valid) → ALLOW // Correct OnUpdate: validates newTenant (invalid) → DENY // After malformed regex is stored, all ingress hostnames are rejected: matched, _ := regexp.MatchString(`[invalid-regex(`, "app.example.com") // matched = false, error ignored → Ingress blocked ``` ##### Fix Swap the parameter names in `hostname_regex.go` to match the interface contract: ```go // BEFORE (buggy) func (h *hostnameRegexHandler) OnUpdate( _ client.Client, _ client.Reader, old *capsulev1beta2.Tenant, tnt *capsulev1beta2.Tenant, ... // AFTER (fixed) func (h *hostnameRegexHandler) OnUpdate( _ client.Client, _ client.Reader, tnt *capsulev1beta2.Tenant, old *capsulev1beta2.Tenant, ... ``` ##### Impact A Cluster Admin (or a compromised admin account) can — intentionally or via a typo — set a malformed `AllowedHostnames.Regex` on any Tenant. The webhook silently accepts the update. All users in the affected tenant are subsequently unable to create or update any Ingress resource until an admin manually corrects the Tenant spec. This constitutes a targeted Denial of Service against the tenant's ingress layer. ## Affected packages | Package | Ecosystem | PURL | Vulnerable versions | Fixed in | | --- | --- | --- | --- | --- | | github.com/projectcapsule/capsule | Go | `pkg:golang/github.com/projectcapsule/capsule` | >= 0.13.0, < 0.13.7 | 0.13.7 | ## Fix commits - Patch: https://github.com/projectcapsule/capsule/commit/8d89d6865df6f41c7faa22fc9e807a57b01bfd0e - Pull request: https://github.com/projectcapsule/capsule/pull/1983 ## Questions **What is the GHSA ID for CVE-2026-61795?** GitHub tracks CVE-2026-61795 as GHSA-f94q-w3w8-cj67. **What is the CVSS score of CVE-2026-61795?** CVE-2026-61795 has a CVSS 3.1 base score of 6.8 (Medium), vector CVSS:3.1/AV:N/AC:L/PR:H/UI:N/S:C/C:N/I:N/A:H. **Which versions are affected by CVE-2026-61795?** github.com/projectcapsule/capsule (Go): >= 0.13.0, < 0.13.7. **How do I fix CVE-2026-61795?** Upgrade to 0.13.7 or later. The fix is in commit 8d89d68 and pull request #1983. **What is the Package URL (PURL) for CVE-2026-61795?** The affected package's PURL is pkg:golang/github.com/projectcapsule/capsule. **Is CVE-2026-61795 exploited in the wild?** CISA's Known Exploited Vulnerabilities catalog doesn't list CVE-2026-61795. That means no confirmed exploitation has been catalogued, not that it is safe to leave unpatched. EPSS estimates a 0.32% chance of exploitation in the next 30 days, higher than 26% of CVEs. ## References - https://github.com/projectcapsule/capsule/pull/1983 (fix) - https://github.com/projectcapsule/capsule/commit/8d89d6865df6f41c7faa22fc9e807a57b01bfd0e (fix) - https://github.com/projectcapsule/capsule/security/advisories/GHSA-f94q-w3w8-cj67 (advisory) - https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/61xxx/CVE-2026-61795.json (advisory) - https://nvd.nist.gov/vuln/detail/CVE-2026-61795 (advisory) - https://github.com/advisories/GHSA-f94q-w3w8-cj67 (advisory) - https://github.com/projectcapsule/capsule (package) - https://github.com/projectcapsule/capsule/releases/tag/v0.13.7 --- Source: CVEminer (https://cveminer.com/vulnerabilities/CVE-2026-61795), compiled from OSV (GitHub advisory), GitHub Advisory Database, OSV (CVE record), CVE.org, CISA KEV catalog. OSV and GitHub Advisory Database content is licensed CC BY 4.0.