{
  "affected": [
    {
      "package": {
        "ecosystem": "Go",
        "name": "go.opentelemetry.io/otel/sdk"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "1.10.0"
            },
            {
              "fixed": "1.33.0"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    }
  ],
  "aliases": [
    "CVE-2026-81869"
  ],
  "database_specific": {
    "cwe_ids": [
      "CWE-176",
      "CWE-400"
    ],
    "github_reviewed": true,
    "github_reviewed_at": "2026-09-29T17:59:10Z",
    "nvd_published_at": "2026-09-16T21:17:22Z",
    "severity": "MODERATE"
  },
  "details": "### Summary\n\nThe OpenTelemetry Go SDK trace package can fail to enforce `AttributeValueLengthLimit` for string attributes containing the valid Unicode replacement character U+FFFD. An oversized attacker-controlled attribute value that includes U+FFFD is returned untruncated, bypassing the configured memory/DoS protection and allowing increased per-span memory usage. The finding is low severity because it requires a deployment with attribute value length limits enabled and attacker-controlled data being recorded into span attributes.\n\nIntroduced in commit 49a6536\n\n### Details\n\nString and string-slice span attributes are truncated through `safeTruncate` when `AttributeValueLengthLimit` is non-negative. The finding evidence identifies this enforcement path in `sdk/trace/span.go:303-331`, with string attributes passed to `safeTruncate` at `sdk/trace/span.go:309-310` and string-slice entries passed to `safeTruncate` in the loop beginning at `sdk/trace/span.go:312`.\n\n`safeTruncate` first calls `safeTruncateValidUTF8`; if that returns `ok=false`, it calls `strings.ToValidUTF8(input, \"\")` and retries. The relevant code is identified in `sdk/trace/span.go:337-355`. `safeTruncateValidUTF8` treats any `utf8.RuneError` from `utf8.DecodeRuneInString` as invalid UTF-8 and immediately returns the original input with `ok=false`. However, Go also returns `utf8.RuneError` for a valid encoded U+FFFD rune. The validation artifact confirms this behavior with output `r=U+FFFD size=3 runeError=true`.\n\nFor an input such as `\"AAAA\" + U+FFFD + strings.Repeat(\"B\", 20)` and a limit of 5, the first truncation attempt sees U+FFFD as `utf8.RuneError` and returns the full input with `ok=false`. `strings.ToValidUTF8` does not remove the valid U+FFFD rune, so the second attempt returns the same full input. As a result, the span attribute value remains 27 bytes long even though the configured limit is 5.\n\n### PoC\n\n[validation-artifact.zip](https://github.com/user-attachments/files/27494267/validation-artifact.zip)\n\n\nThe validation artifact contains a package-level Go test at `validation-artifact.tar:safe_truncate_bypass/safe_truncate_poc_test.go` and supporting output at `validation-artifact.tar:safe_truncate_bypass/runecheck_output.txt`.\n\nReproduction configuration:\n- Repository: `pellared/opentelemetry-go`\n- Commit: `49a6536` from September 12, 2022\n- Package/module path: `sdk/trace` under the `sdk` module\n- Attribute value length limit used by the PoC: `limit := 5`\n- Dependencies must be available through the network or a local module cache/vendor directory.\n\nCommands:\n```sh\ncd /path/to/opentelemetry-go\ngit checkout 49a6536\ntar -xOf /path/to/validation-artifact.tar safe_truncate_bypass/safe_truncate_poc_test.go \u003e sdk/trace/safe_truncate_poc_test.go\ncd sdk\ngo test ./trace -run TestSafeTruncateBypass -count=1 -v\n```\n\nExpected vulnerable output includes a failing test showing that the returned value exceeds the configured limit:\n```text\n=== RUN   TestSafeTruncateBypass\n    safe_truncate_poc_test.go:14: input_len=27 got_len=27 input=\"AAAA\ufffdBBBBBBBBBBBBBBBBBBBB\" got=\"AAAA\ufffdBBBBBBBBBBBBBBBBBBBB\"\n    safe_truncate_poc_test.go:16: bypass: got_len 27 \u003e limit 5\n--- FAIL: TestSafeTruncateBypass\n```\n\nThe artifact also records the standalone UTF-8 behavior needed for the bypass:\n```sh\ntar -xOf /path/to/validation-artifact.tar safe_truncate_bypass/runecheck_output.txt\n```\n\nExpected output:\n```text\nr=U+FFFD size=3 runeError=true\n```\n\n### Impact\n\nThis is a Unicode handling and resource-limit bypass that weakens span attribute memory controls. Applications that enable `AttributeValueLengthLimit` to bound memory usage can still store oversized attacker-controlled attribute values if those values contain U+FFFD. The practical impact is increased memory use and reduced denial-of-service protection in the instrumented process; the finding does not show confidentiality or integrity impact.",
  "id": "GHSA-p9f8-wvj8-2fg8",
  "modified": "2026-09-29T17:59:10Z",
  "published": "2026-09-29T17:59:10Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://github.com/open-telemetry/opentelemetry-go/security/advisories/GHSA-p9f8-wvj8-2fg8"
    },
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-81869"
    },
    {
      "type": "WEB",
      "url": "https://github.com/open-telemetry/opentelemetry-go/issues/5996"
    },
    {
      "type": "WEB",
      "url": "https://github.com/open-telemetry/opentelemetry-go/pull/5997"
    },
    {
      "type": "WEB",
      "url": "https://github.com/open-telemetry/opentelemetry-go/commit/e016a78c9f5b24a1c2beeaad47686c2f2213f49a"
    },
    {
      "type": "PACKAGE",
      "url": "https://github.com/open-telemetry/opentelemetry-go"
    },
    {
      "type": "WEB",
      "url": "https://github.com/open-telemetry/opentelemetry-go/releases/tag/sdk/v1.33.0"
    }
  ],
  "schema_version": "1.4.0",
  "severity": [
    {
      "score": "CVSS:4.0/AV:L/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:L/SC:N/SI:N/SA:N",
      "type": "CVSS_V4"
    }
  ],
  "summary": "OpenTelemetry-Go: UTF-8 replacement rune bypasses attribute length truncation"
}