# OpenTelemetry-Go: UTF-8 replacement rune bypasses attribute length truncation

Advisory record · `GHSA-p9f8-wvj8-2fg8`

- **Identifiers:** `GHSA-p9f8-wvj8-2fg8` · `CVE-2026-81869` · `GO-2026-6616`
- **State:** Confirmed
- **Severity:** CVSS 5.1 Medium
- **Critical:** No
- **Weakness (CWE):** [CWE-176](https://cwe.mitre.org/data/definitions/176.html) · [CWE-400](https://cwe.mitre.org/data/definitions/400.html)
- **Tags:** [Denial of service](https://agentprime.io/advisories/tag/dos.md) · [CWE-176](https://agentprime.io/advisories/tag/cwe-176.md)
- **Published:** 29 Sept 2026
- **Updated:** 1 Oct 2026
- **Reviewed by a person:** No

Published by the GitHub Advisory Database at 29 Sept 2026, 17:59 UTC. agentprime has not analysed this yet, so whether it affects any app is not known.

## Affected packages

- `go.opentelemetry.io/otel/sdk` (Go): affected `>=1.10.0, <1.33.0`; fixed in `1.33.0`

## Machine-written summary

Summary written by Claude Haiku from the source advisory. Not reviewed by a person.

> Versions 1.10.0 up to but not including 1.33.0 of go.opentelemetry.io/otel/sdk do not fully enforce the AttributeValueLengthLimit setting on string span attributes that contain the Unicode replacement character U+FFFD. An attacker who can get attacker-controlled data recorded into span attributes, in a deployment where the limit is enabled, can cause oversized values to be stored untruncated, increasing per-span memory use. Upgrade to version 1.33.0 or later. The source gives no workaround.

Written 1 Nov 2026.

## Not analysed yet

We haven’t published our analysis of this Advisory yet. Once a person has reviewed it, this page will say what’s vulnerable, what has to be true for your app to be affected, and how to check.

## Severity and exploitation

- 5.1 Medium, CVSS 4.0: `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`, from CNA (GitHub_M)

- **CISA KEV:** Not listed.
- **EPSS:** 0.0018, the 7th percentile, on 6 Nov 2026: FIRST’s estimate of the chance of exploitation in the next 30 days.

## Timeline

- 31 Oct 2026, 14:12 UTC: First seen by agentprime
- 31 Oct 2026, 14:12 UTC: [Confirmed by OSV](https://osv.dev/vulnerability/GHSA-p9f8-wvj8-2fg8)

## Sources

- [GitHub Advisory Database: GHSA-p9f8-wvj8-2fg8](https://github.com/advisories/GHSA-p9f8-wvj8-2fg8)
- [OSV: GHSA-p9f8-wvj8-2fg8](https://osv.dev/vulnerability/GHSA-p9f8-wvj8-2fg8)
- <https://github.com/open-telemetry/opentelemetry-go/security/advisories/GHSA-p9f8-wvj8-2fg8>
- <https://nvd.nist.gov/vuln/detail/CVE-2026-81869>
- <https://github.com/open-telemetry/opentelemetry-go/issues/5996>
- <https://github.com/open-telemetry/opentelemetry-go/pull/5997>
- <https://github.com/open-telemetry/opentelemetry-go/commit/e016a78c9f5b24a1c2beeaad47686c2f2213f49a>
- <https://github.com/open-telemetry/opentelemetry-go>
- <https://github.com/open-telemetry/opentelemetry-go/releases/tag/sdk/v1.33.0>

Facts on this page come from the GitHub Advisory Database (CC-BY 4.0), OSV and the other sources listed, as published. We don’t reproduce full advisory descriptions, which can contain exploit code.

## Check whether this affects you

A Match means an installed version is in the affected range above. Most don’t affect the app; agentprime hasn’t analysed this one yet.

- With the agentprime MCP server (<https://api.agentprime.io/mcp>), ask your agent to check the project: `check_lockfile` sends a lockfile, `check_packages` a list of installed packages, and both return the Matches and the upgrades that clear them. `get_advisory` returns this record. Setup: <https://agentprime.io/mcp.md>
- In a browser: <https://agentprime.io/check/> reads your lockfile in the browser, never uploading it.
- Whether it touches your code, with file and line: the Claude Code plugin, <https://agentprime.io/plugin.md>
- As JSON: <https://api.agentprime.io/v1/advisories/GHSA-p9f8-wvj8-2fg8>, or `POST https://api.agentprime.io/v1/match` with your packages (<https://agentprime.io/api.md>)

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The web page: <https://agentprime.io/advisories/GHSA-p9f8-wvj8-2fg8/>. Everything for agents: <https://agentprime.io/llms.txt>.