CVE-2026-54511: @logtape/syslog Syslog Log Injection Vulnerability

{
  "schema_version" : "1.4.0",
  "id" : "GHSA-8h6h-x5pq-56fq",
  "modified" : "2026-08-26T14:28:04Z",
  "published" : "2026-08-26T14:28:04Z",
  "aliases" : [ "CVE-2026-54511" ],
  "summary" : "@logtape/syslog: syslog log injection via unescaped control characters and unvalidated SD-NAME keys",
  "details" : "`@logtape/syslog` contains two related output-encoding bugs in the structured data formatting code. Both only affect deployments with `includeStructuredData: true`, which is non-default.\n\n## 1. Unescaped C0 control characters in structured data values\n\n`escapeStructuredDataValue()` in `packages/syslog/src/syslog.ts` escapes `\\`, `\"`, and `]` per RFC 5424 but does not escape newline (`\\n`), carriage return (`\\r`), or any other C0 control characters (U+0000–U+001F):\n\n```typescript\nfunction escapeStructuredDataValue(value: string): string {\n  return value\n    .replace(/\\\\/g, \"\\\\\\\\\")\n    .replace(/\"/g, '\\\\\"')\n    .replace(/]/g, \"\\\\]\");\n  // \\n, \\r, and other C0 control characters are not escaped\n}\n```\n\nTCP syslog commonly uses `\\n` as a frame delimiter (RFC 6587, non-transparent framing). If an attacker-controlled value contains a literal newline, that newline terminates the current syslog frame. Bytes following the newline begin a new frame, and if they form a valid RFC 5424 header (`<PRI>1 …`), a downstream collector will accept them as a separate, authentic-looking syslog record.\n\n## 2. Unvalidated SD-NAME keys\n\nStructured data parameter keys are inserted into the message without validation or escaping:\n\n```typescript\nelements.push(`${key}=\"${escapedValue}\"`);\n```\n\nRFC 5424 defines SD-NAME as printable US-ASCII characters excluding `=`, `]`, `\"`, and space, with a maximum length of 32. A key containing any of those characters, control characters, or exceeding the length limit will produce malformed structured data. If the key itself contains an embedded `]`, it can prematurely close the structured-data element.\n\nIn typical usage, property keys are developer-defined string literals and therefore safe. However, if an application forwards attacker-controlled keys as log properties—for example by spreading request headers or arbitrary metadata into a log record—this becomes a second injection path.\n\n## Proof of concept\n\nThe following Node.js snippet (no dependencies, no network required) demonstrates that the escaped value still contains a literal newline:\n\n```javascript\nfunction escapeStructuredDataValue(value) {\n  return value\n    .replace(/\\\\/g, \"\\\\\\\\\")\n    .replace(/\"/g, '\\\\\"')\n    .replace(/]/g, \"\\\\]\");\n}\n\nconst payload =\n  'normal\\n<134>1 2026-01-01T00:00:00Z forged evil - - - INJECTED';\n\nconst result = escapeStructuredDataValue(payload);\nconsole.log(\"Newline present after escape:\", result.includes(\"\\n\")); // true\n```\n\nTested with Node.js 22.17.1.\n\n## Impact\n\nAn attacker who controls log property values can:\n\n- forge syslog records attributed to arbitrary hosts, applications, or process IDs;\n- insert records with arbitrary severity or facility levels;\n- obscure malicious activity by injecting misleading entries around legitimate ones;\n- break downstream log parsers or SIEM correlation rules that rely on log integrity.\n\nAffected downstream collectors include rsyslog, syslog-ng, Splunk, Elastic Stack, and any other system using RFC 6587 non-transparent framing.\n\n## Suggested fix\n\n### Structured data values\n\nEscape all C0 control characters (U+0000–U+001F) in addition to `\\`, `\"`, and `]`. RFC 5424 does not define an escape sequence for control characters in PARAM-VALUE; the most interoperable approach is to strip or replace them:\n\n```typescript\nfunction escapeStructuredDataValue(value: string): string {\n  return value\n    .replace(/\\\\/g, \"\\\\\\\\\")\n    .replace(/\"/g, '\\\\\"')\n    .replace(/]/g, \"\\\\]\")\n    .replace(/[\\x00-\\x1f]/g, (c) =>\n      `\\\\x${c.charCodeAt(0).toString(16).padStart(2, \"0\")}`\n    );\n}\n```\n\nAlternatively, strip them entirely: `.replace(/[\\x00-\\x1f]/g, \"\")`. The right choice depends on whether downstream consumers need some representation of the original value.\n\n### SD-NAME keys\n\nValidate each key against the RFC 5424 SD-NAME grammar before including it. Keys that fail validation should be skipped or sanitized:\n\n```typescript\n// SD-NAME: printable US-ASCII, excluding '=', ']', '\"', SP; max 32 chars\nconst SD_NAME_RE = /^[!-<>-Z\\\\^-z|~]{1,32}$/;\n\nfor (const [key, value] of Object.entries(record.properties)) {\n  if (!SD_NAME_RE.test(key)) continue;\n  const escapedValue = escapeStructuredDataValue(String(value));\n  elements.push(`${key}=\"${escapedValue}\"`);\n}\n```",
  "severity" : [ {
    "type" : "CVSS_V3",
    "score" : "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:N/I:H/A:N"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "npm",
      "name" : "@logtape/syslog"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "2.1.0"
      }, {
        "fixed" : "2.1.5"
      } ]
    } ],
    "database_specific" : {
      "last_known_affected_version_range" : "<= 2.1.4"
    }
  }, {
    "package" : {
      "ecosystem" : "npm",
      "name" : "@logtape/syslog"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "2.0.0"
      }, {
        "fixed" : "2.0.14"
      } ]
    } ]
  }, {
    "package" : {
      "ecosystem" : "npm",
      "name" : "@logtape/syslog"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0"
      }, {
        "fixed" : "1.3.11"
      } ]
    } ]
  } ],
  "references" : [ {
    "type" : "WEB",
    "url" : "https://github.com/dahlia/logtape/security/advisories/GHSA-8h6h-x5pq-56fq"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/dahlia/logtape/commit/7a6e5b9ddf7915edfff78fa129bc17c979b2a623"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/dahlia/logtape"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/dahlia/logtape/releases/tag/1.3.11"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/dahlia/logtape/releases/tag/2.0.14"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/dahlia/logtape/releases/tag/2.1.5"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-117", "CWE-93" ],
    "severity" : "HIGH",
    "github_reviewed" : true,
    "github_reviewed_at" : "2026-08-26T14:28:04Z",
    "nvd_published_at" : null
  }
}