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Fencer Vulns
medium 5.1

CVE-2026-81869 json

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

published 2026-09-16 53 d ago modified 2026-10-01 38 d ago also GHSA-p9f8-wvj8-2fg8 , GO-2026-6616 , EUVD-2026-81260

cvss
5.1
version 4.0, CNA
cisa kev
Not listed
not in CISA's catalog
epss
0.2%
EPSS 0.2% chance of exploitation in 30 days, percentile 7%
public exploits
0
none known

Summary

OpenTelemetry-Go is the Go implementation of OpenTelemetry. From version 1.10.0 until 1.33.0, the sdk/trace/span.go attribute truncation path can fail to enforce AttributeValueLengthLimit for string and string-slice attributes containing the valid Unicode replacement character U+FFFD. safeTruncateValidUTF8 treats the valid replacement rune as invalid UTF-8 and returns the original input, while strings.ToValidUTF8 leaves that valid rune unchanged, so a second safeTruncate attempt can also return the oversized value. An attacker who controls span attribute content can retain values longer than the configured limit, increasing per-span memory use and weakening denial-of-service protection in the instrumented process. This issue is fixed in version 1.33.0.

Patch / fix

  • go go.opentelemetry.io/otel/sdk 1.33.0
  • golang-opentelemetry-otel Debian 14 1.43.0-1

debian advisories DEBIAN-CVE-2026-81869

  • cert-manager Azure Linux 3.0 1.12.15-14
  • docker-compose Azure Linux 3.0 2.27.0-15
  • flannel Azure Linux 3.0 0.24.2-33
  • kube-vip-cloud-provider Azure Linux 3.0 0.0.10-10
  • moby-containerd-cc Azure Linux 3.0 1.7.7-18
  • moby-engine Azure Linux 3.0 25.0.18-1
  • opa Azure Linux 3.0 0.63.0-6

azure linux advisories AZL-103143AZL-103161AZL-103170AZL-103233AZL-103239AZL-103245

Azure Linux vulnerability data, Copyright (c) Microsoft Corporation, from https://github.com/microsoft/AzureLinuxVulnerabilityData via OSV, under the MIT licence; changed: normalised to fixed package versions per release. MIT

Vendor advisories

What the vendors themselves say about their products: affected, fixed or not affected, and what to do.

red hat product security vex CVE-2026-81869 updated cvss 4.0

github.com/open-telemetry/opentelemetry-go: OpenTelemetry-Go: Denial of Service via attribute length truncation bypass

  • Red Hat All currently supported Red Hat products
    not affected: vulnerable code not present

Red Hat CSAF VEX © Red Hat, Inc., from https://security.access.redhat.com/data/csaf/v2/vex/; changed: reduced to product statuses and remediations. CC BY 4.0 · csaf

CISA SSVC

Exploitation
Proof of concept is public
Automatable
no
Technical impact
partial
Assessed
52 d ago

Exploit prediction

0.18% chance of exploitation in the next 30 days, higher than 7% of all scored CVEs (FIRST EPSS, 2026-11-08).

Exploits and checks

  • github.com https://github.com/open-telemetry/opentelemetry-go/security/advisories/GHSA-p9f8-wvj8-2fg8 referenced PoC, tagged "exploit" by a source, unverified

CVSS scores

assigned by version score vector
CNA 4.0 5.1 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
CNA 4.0 5.1 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/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X

Affected packages

ecosystem package affected fixed in
go go.opentelemetry.io/otel/sdk
>=1.10.0, <1.33.0
1.33.0

Affected products

  • open-telemetry opentelemetry-go

Classification

Weakness
  • CWE-176 Improper Handling of Unicode Encoding
  • CWE-400 Uncontrolled Resource Consumption

References

Sources

Fencer Vulns keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.