Vulnerability-Lookup

CVE-2026-46430 (GCVE-0-2026-46430)

Vulnerability from cvelistv5 – Published: 2026-05-26 16:41 – Updated: 2026-05-26 18:57

Title

Algernon: Auto-refresh SSE event server binds to all interfaces by default on Linux/macOS

Summary

Algernon is a small self-contained pure-Go web server. Prior to 1.17.7, the SSE event server bound to 0.0.0.0:5553 on Linux/macOS by default because the platform-dependent host default in engine/flags.go:39-46 set host = "" for non-Windows, and utils.JoinHostPort("", ":5553") resolves to ":5553". This vulnerability is fixed in 1.17.7.

Severity

4.3 (Medium)


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

SSVC

Exploitation: poc Automatable: no Technical Impact: partial

CISA Coordinator · CISA-ADP (v2.0.3)

Decision recorded 2026-05-26 18:57 UTC

CWE

CWE-668 - Exposure of Resource to Wrong Sphere
CWE-1188 - Insecure Default Initialization of Resource

Assigner

GitHub_M mitre root

References

1 reference

URL	Tags
https://github.com/xyproto/algernon/security/advi…	x_refsource_CONFIRM

Impacted products

1 product

Vendor	Product	Version	CPE status
xyproto	algernon	Affected: < 1.17.7	guessed

Show details on NVD website

JSON

To clipboard

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FKIE_CVE-2026-46430

Vulnerability from fkie_nvd - Published: 2026-05-26 17:16 - Updated: 2026-07-24 11:10

Severity

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

Summary

References

	URL	Tags
	security-advisories@github.com	https://github.com/xyproto/algernon/security/advisories/GHSA-gj84-924c-48fx
	134c704f-9b21-4f2e-91b3-4a467353bcc0	https://github.com/xyproto/algernon/security/advisories/GHSA-gj84-924c-48fx

Impacted products

	Vendor	Product	Version

JSON

To clipboard

{
  "affected": [
    {
      "affectedData": [
        {
          "product": "algernon",
          "vendor": "xyproto",
          "versions": [
            {
              "status": "affected",
              "version": "\u003c 1.17.7"
            }
          ]
        }
      ],
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    }
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    {
      "lang": "en",
      "value": "Algernon is a small self-contained pure-Go web server. Prior to 1.17.7, the SSE event server bound to 0.0.0.0:5553 on Linux/macOS by default because the platform-dependent host default in engine/flags.go:39-46 set host = \"\" for non-Windows, and utils.JoinHostPort(\"\", \":5553\") resolves to \":5553\". This vulnerability is fixed in 1.17.7."
    },
    {
      "lang": "es",
      "value": "Algernon es un peque\u00f1o servidor web autocontenido y puro Go. Antes de la versi\u00f3n 1.17.7, el servidor de eventos SSE se enlazaba a 0.0.0.0:5553 en Linux/macOS por defecto porque el valor predeterminado del host dependiente de la plataforma en engine/flags.go:39-46 establec\u00eda host = \"\" para sistemas que no eran Windows, y utils.JoinHostPort(\"\", \":5553\") se resuelve como \":5553\". Esta vulnerabilidad se corrige en la versi\u00f3n 1.17.7."
    }
  ],
  "id": "CVE-2026-46430",
  "lastModified": "2026-07-24T11:10:00.170",
  "metrics": {
    "cvssMetricV31": [
      {
        "cvssData": {
          "attackComplexity": "LOW",
          "attackVector": "ADJACENT_NETWORK",
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          "baseScore": 4.3,
          "baseSeverity": "MEDIUM",
          "confidentialityImpact": "LOW",
          "integrityImpact": "NONE",
          "privilegesRequired": "NONE",
          "scope": "UNCHANGED",
          "userInteraction": "NONE",
          "vectorString": "CVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:N",
          "version": "3.1"
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}

GHSA-GJ84-924C-48FX

Vulnerability from github – Published: 2026-05-20 15:33 – Updated: 2026-05-20 15:33

Summary

Algernon: Auto-refresh SSE event server binds to all interfaces by default on Linux/macOS

Details

Summary

The SSE event server bound to 0.0.0.0:5553 on Linux/macOS by default because the platform-dependent host default in engine/flags.go:39-46 set host = "" for non-Windows, and utils.JoinHostPort("", ":5553") resolves to ":5553" — a Go http.Server.Addr of ":5553" listens on every interface. On Windows the same code chose "localhost", binding loopback only.

The result was a platform split where the OS Algernon's dev workflow is most often used on (Linux/macOS) got the network-exposed default, and only Windows users got the loopback-safe one. A LAN peer with no developer interaction could connect to <dev-laptop-ip>:5553 and read the file-change stream.

This advisory covers the bind-address default in isolation. The fix is independent of authentication (#2a) and CORS (#2b) — switching the default to loopback can be done without touching either.

Details

Root cause — platform-dependent `host` default in `handleFlags`

// engine/flags.go:39-46  (1.17.6)
host := ""
if runtime.GOOS == "windows" {
    host = "localhost"
    // Default Bolt database file
    ac.defaultBoltFilename = filepath.Join(serverTempDir, "algernon.db")
    // Default log file
    ac.defaultLogFile = filepath.Join(serverTempDir, "algernon.log")
}

// engine/config.go:388-391  (1.17.6, finalConfiguration)
if ac.eventAddr == "" {
    ac.eventAddr = utils.JoinHostPort(host, ac.defaultEventColonPort)
}

Result tabulated:

Platform	`host`	`eventAddr` after `JoinHostPort`	Effective bind
Linux	`""`	`":5553"`	`0.0.0.0:5553` (all interfaces)
macOS	`""`	`":5553"`	`0.0.0.0:5553` (all interfaces)
Windows	`"localhost"`	`"localhost:5553"`	`127.0.0.1:5553` (loopback)

The same host value also governs the main web server bind, so the platform split affects both ports. The web-server bind on Linux/macOS is a separate (defensible) design decision — a server intended to be reachable; the SSE port is not such a service and inherited the same default by accident.

Why this is an independent finding

The fix is a single line: change the default host value, or change the eventAddr default specifically, to "localhost" regardless of platform. No change to authentication or CORS is required to close the network-reach half of the original bundled advisory. A LAN peer can no longer connect — the listener is unreachable from another host — even if the SSE handler still has no authentication and still returns Allow-Origin: *.

PoC (against 1.17.6 on Linux/macOS)

# Operator's laptop on a hotel/cafe/office WiFi:
algernon -a /path/to/project
# => SSE listener bound to 0.0.0.0:5553

# Any peer on the same subnet:
$ curl -sN http://<dev-laptop-ip>:5553/sse
id: 0
data: /path/to/project/secret-notes.md

id: 1
data: /path/to/project/.env.local

No interaction from the developer is required. The peer needs network reach and nothing else.

Impact

Confidentiality: medium. LAN-bounded continuous information disclosure of filenames and edit timing.
Integrity: none.
Availability: none directly.

The CVSS vector uses AV:A (adjacent network) to model the LAN-only reach. The vector for a misconfigured deployment behind a NAT-less or routed network would shift to AV:N and rise to 5.3.

Suggestions to fix

Primary fix — pick localhost as the SSE default on every platform.

// engine/flags.go -- platform-independent default for the event listener
// (keep the existing platform split for the WEB server if desired, but
// not for the event server)
host := "localhost"

Or, more surgically:

// engine/config.go -- finalConfiguration
if ac.eventAddr == "" {
    ac.eventAddr = utils.JoinHostPort("localhost", ac.defaultEventColonPort)
}

An operator who genuinely wants LAN-reachable SSE can pass --eventserver 0.0.0.0:5553 explicitly and accept the consequences.

Stronger fix — eliminate the second listener entirely. Mount the SSE handler on the main mux at /sse. The bind address is then whatever the main server uses; there is no second listener and therefore no second bind-address default to get wrong.

Live verification

Audit-host bind check (Windows 10):

$ netstat -an | findstr 5553
  TCP    127.0.0.1:5553         0.0.0.0:0              LISTENING

Confirms the Windows default is localhost. The Linux/macOS bind to 0.0.0.0:5553 is documented in the code path above; it was not exercised on the audit machine because the audit host was Windows. A maintainer reproducing on a Linux host would see 0.0.0.0:5553 LISTENING from ss -tlnp.

Severity

4.3 (Medium)


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

Show details on source website

JSON

To clipboard

{
  "affected": [
    {
      "database_specific": {
        "last_known_affected_version_range": "\u003c= 1.17.6"
      },
      "package": {
        "ecosystem": "Go",
        "name": "github.com/xyproto/algernon"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            },
            {
              "fixed": "1.17.7"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    }
  ],
  "aliases": [
    "CVE-2026-46430"
  ],
  "database_specific": {
    "cwe_ids": [
      "CWE-1188",
      "CWE-668"
    ],
    "github_reviewed": true,
    "github_reviewed_at": "2026-05-20T15:33:56Z",
    "nvd_published_at": null,
    "severity": "MODERATE"
  },
  "details": "### Summary\n\nThe SSE event server bound to `0.0.0.0:5553` on Linux/macOS by default because the platform-dependent host default in `engine/flags.go:39-46` set `host = \"\"` for non-Windows, and `utils.JoinHostPort(\"\", \":5553\")` resolves to `\":5553\"` \u2014 a Go `http.Server.Addr` of `\":5553\"` listens on every interface. On Windows the same code chose `\"localhost\"`, binding loopback only.\n\nThe result was a platform split where the OS Algernon\u0027s dev workflow is most often used on (Linux/macOS) got the network-exposed default, and only Windows users got the loopback-safe one. A LAN peer with no developer interaction could connect to `\u003cdev-laptop-ip\u003e:5553` and read the file-change stream.\n\nThis advisory covers the bind-address default in isolation. The fix is independent of authentication (#2a) and CORS (#2b) \u2014 switching the default to loopback can be done without touching either.\n\n### Details\n\n#### Root cause \u2014 platform-dependent `host` default in `handleFlags`\n\n```go\n// engine/flags.go:39-46  (1.17.6)\nhost := \"\"\nif runtime.GOOS == \"windows\" {\n    host = \"localhost\"\n    // Default Bolt database file\n    ac.defaultBoltFilename = filepath.Join(serverTempDir, \"algernon.db\")\n    // Default log file\n    ac.defaultLogFile = filepath.Join(serverTempDir, \"algernon.log\")\n}\n```\n\n```go\n// engine/config.go:388-391  (1.17.6, finalConfiguration)\nif ac.eventAddr == \"\" {\n    ac.eventAddr = utils.JoinHostPort(host, ac.defaultEventColonPort)\n}\n```\n\nResult tabulated:\n\n| Platform | `host` | `eventAddr` after `JoinHostPort` | Effective bind |\n|---|---|---|---|\n| Linux | `\"\"` | `\":5553\"` | `0.0.0.0:5553` (all interfaces) |\n| macOS | `\"\"` | `\":5553\"` | `0.0.0.0:5553` (all interfaces) |\n| Windows | `\"localhost\"` | `\"localhost:5553\"` | `127.0.0.1:5553` (loopback) |\n\nThe same `host` value also governs the main web server bind, so the platform split affects both ports. The web-server bind on Linux/macOS is a separate (defensible) design decision \u2014 a server intended to be reachable; the SSE port is *not* such a service and inherited the same default by accident.\n\n#### Why this is an independent finding\n\nThe fix is a single line: change the default `host` value, or change the `eventAddr` default specifically, to `\"localhost\"` regardless of platform. No change to authentication or CORS is required to close the network-reach half of the original bundled advisory. A LAN peer can no longer connect \u2014 the listener is unreachable from another host \u2014 even if the SSE handler still has no authentication and still returns `Allow-Origin: *`.\n\n### PoC (against 1.17.6 on Linux/macOS)\n\n```bash\n# Operator\u0027s laptop on a hotel/cafe/office WiFi:\nalgernon -a /path/to/project\n# =\u003e SSE listener bound to 0.0.0.0:5553\n\n# Any peer on the same subnet:\n$ curl -sN http://\u003cdev-laptop-ip\u003e:5553/sse\nid: 0\ndata: /path/to/project/secret-notes.md\n\nid: 1\ndata: /path/to/project/.env.local\n```\n\nNo interaction from the developer is required. The peer needs network reach and nothing else.\n\n### Impact\n\n- **Confidentiality:** medium. LAN-bounded continuous information disclosure of filenames and edit timing.\n- **Integrity:** none.\n- **Availability:** none directly.\n\nThe CVSS vector uses `AV:A` (adjacent network) to model the LAN-only reach. The vector for a misconfigured deployment behind a NAT-less or routed network would shift to `AV:N` and rise to 5.3.\n\n### Suggestions to fix\n\n**Primary fix \u2014 pick `localhost` as the SSE default on every platform.**\n\n```go\n// engine/flags.go -- platform-independent default for the event listener\n// (keep the existing platform split for the WEB server if desired, but\n// not for the event server)\nhost := \"localhost\"\n```\n\nOr, more surgically:\n\n```go\n// engine/config.go -- finalConfiguration\nif ac.eventAddr == \"\" {\n    ac.eventAddr = utils.JoinHostPort(\"localhost\", ac.defaultEventColonPort)\n}\n```\n\nAn operator who genuinely wants LAN-reachable SSE can pass `--eventserver 0.0.0.0:5553` explicitly and accept the consequences.\n\n**Stronger fix \u2014 eliminate the second listener entirely.** Mount the SSE handler on the main mux at `/sse`. The bind address is then whatever the main server uses; there is no second listener and therefore no second bind-address default to get wrong.\n\n### Live verification\n\nAudit-host bind check (Windows 10):\n\n```\n$ netstat -an | findstr 5553\n  TCP    127.0.0.1:5553         0.0.0.0:0              LISTENING\n```\n\nConfirms the Windows default is `localhost`. The Linux/macOS bind to `0.0.0.0:5553` is documented in the code path above; it was not exercised on the audit machine because the audit host was Windows. A maintainer reproducing on a Linux host would see `0.0.0.0:5553 LISTENING` from `ss -tlnp`.",
  "id": "GHSA-gj84-924c-48fx",
  "modified": "2026-05-20T15:33:56Z",
  "published": "2026-05-20T15:33:56Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://github.com/xyproto/algernon/security/advisories/GHSA-gj84-924c-48fx"
    },
    {
      "type": "PACKAGE",
      "url": "https://github.com/xyproto/algernon"
    }
  ],
  "schema_version": "1.4.0",
  "severity": [
    {
      "score": "CVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:N",
      "type": "CVSS_V3"
    }
  ],
  "summary": "Algernon: Auto-refresh SSE event server binds to all interfaces by default on Linux/macOS"
}

Sightings

Author	Source	Type	Date	Other

Nomenclature

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Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.

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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.
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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-2026-46430 (GCVE-0-2026-46430)

FKIE_CVE-2026-46430

GHSA-GJ84-924C-48FX

Summary

Details

Root cause — platform-dependent host default in handleFlags

Why this is an independent finding

PoC (against 1.17.6 on Linux/macOS)

Impact

Suggestions to fix

Live verification

Tags

Sightings

Nomenclature

Related by attack behaviour

Root cause — platform-dependent `host` default in `handleFlags`