MediumCVE-2026-81871

    OpenTelemetry-Go: Log gRPC exporter ignores env TLS certs, bypassing mTLS/pinning (CVE-2026-81871)

    Published Last modified Sources: Red Hat, SUSE, OSV, CVE.org, Hersteller, Msrc Update Guide

    What is affected, what to do

    A flaw was found in OpenTelemetry-Go, specifically within its gRPC log exporter. This vulnerability allows a network attacker to bypass the intended private Certificate Authority (CA) pinning and mutual Transport Layer Security (TLS) configurations.

    Update Opentelemetry-go to version 0.21.0.

    Affected
    • Opentelemetry-go lt *..0.21.0
    Fixed in
    • Opentelemetry-go 0.21.0

    Not sure whether and how you are affected? Ask a question about this vulnerability

    Metrics

    6.3

    Priority

    XIEM Effective CVSS: highest available CVSS rating from NVD and vendor data.

    Source: Vendor (CNA), CVSS v4

    6.3

    CVSS v4

    Severity Medium on the scale from 0 to 10.

    Source: Red Hat, SUSE, OSV, CVE.org, Hersteller, Msrc Update Guide

    0.2 %

    EPSS score

    Low — model estimates < 1% exploitation likelihood.

    Source: FIRST EPSS, percentile 9.4

    Show all metrics
    Severity
    Medium
    Priority (0–325)

    The priority score is a consolidated metric that condenses several individual signals into a single, action-guiding ranking: technical severity (CVSS), exploitation likelihood (EPSS), known-exploited status (KEV) and the context of the affected asset. The aim is to answer the only truly important question in vulnerability management: what first?

    Read in glossary
    59.51 Methodology
    Exploit maturity

    An exploit is code or a technique that specifically uses a concrete vulnerability to force unintended behaviour — such as executing code or escalating privileges. It is the tool that turns a theoretical flaw into a practical attack.

    Read in glossary
    no public PoC known
    XIEM Effective CVSS

    XIEM® is the tiered managed-security operating model from NEOSEC and a registered trademark of NEOSEC GmbH. It extends classic SIEM — the central collection, normalisation and correlation of security-relevant events — with endpoint forensics, network visibility and deception technology, and consolidates them into three building tiers: Sentry, Orchestrate and Command.

    Read in glossary
    6.3 Methodology
    CVSS v4

    CVSS is the globally established, open standard for assessing the technical severity of a vulnerability on a scale from 0 to 10. It describes how easily a flaw can be exploited and what damage it can cause — but not how likely its actual exploitation is. CVSS and the complementary EPSS deliberately answer different questions.

    Read in glossary
    6.3
    EPSS score

    The EPSS score is the absolute model output for an individual vulnerability: the estimated probability of real-world exploitation within the next 30 days, expressed as a value between 0 and 1 (i.e. 0 % to 100 %). A score of 0.42 means „the model estimates a 42 % chance of real-world exploitation within 30 days“.

    Read in glossary
    0.2 %
    Low — model estimates < 1% exploitation likelihood.
    EPSS percentile

    The EPSS percentile is the relative position of a vulnerability within all EPSS-scored CVEs, expressed as a value between 0 and 1. A percentile of 0.90 means „this CVE has a higher EPSS score than 90 % of all other scored CVEs“. Unlike the EPSS score, it is not a probability — but a positioning within a ranking.

    Read in glossary
    9.4
    Low — this CVE sits in the lower 10% of all CVEs scored today.
    KEV status

    The KEV catalogue is a list maintained by the US authority CISA of vulnerabilities for which active exploitation in the wild has been confirmed. It answers not the question „how severe?“ but „is it already being attacked?“ — thereby sharply prioritising patching.

    Read in glossary
    —
    Published
    CISA assessment (SSVC)
    Exploitation: none known · not automatable · Technical impact: partial
    Source: CISA Vulnrichment, as of 17 September 2026
    CWE

    CWE is a catalogue of typical weakness types in software and hardware — such as flawed input validation, unsafe memory handling or poor authentication. Where a CVE names a concrete vulnerability in a concrete product, a CWE describes the underlying class of defect.

    Read in glossary
    CWE-295, CWE-923

    Detection rules

    No NEOSEC detection rule is available for this vulnerability yet.

    Classification under NIS2 and CRA

    Rule-based classification from exploitation status and severity. It does not replace a case-by-case assessment.

    NIS2

    NIS2 is EU Directive (EU) 2022/2555 to raise the level of cybersecurity across the Union. It substantially broadens obligations compared with the first NIS directive: more sectors, mandatory risk management, staged reporting duties and personal accountability of senior management.

    Read in glossary
    Handle the vulnerability in regular vulnerability handling under Art. 21(2)(e) NIS2.
    CRA

    The CRA is EU Regulation (EU) 2024/2847 setting horizontal cybersecurity requirements for „products with digital elements“ — from industrial controllers and software to connected consumer devices. For the first time manufacturers must ensure security across the entire product lifecycle, handle vulnerabilities and provide security updates.

    Read in glossary
    From 11.12.2027, Annex I Part II CRA requires manufacturers of affected products with digital elements to handle vulnerabilities without delay and provide security updates.
    ISO/IEC 27001

    ISO/IEC 27001 is the internationally leading standard for an information security management system (ISMS). It describes a risk-based, process-oriented framework to systematically plan, implement, review and improve information security.

    Read in glossary
    Control A.8.8, management of technical vulnerabilities: assess relevance to your systems, plan remediation and keep evidence.

    Description

    A flaw was found in OpenTelemetry-Go, specifically within its gRPC log exporter. This vulnerability allows a network attacker to bypass the intended private Certificate Authority (CA) pinning and mutual Transport Layer Security (TLS) configurations. The issue arises because the environment-only TLS path incorrectly uses system-trusted certificates instead of the application's configured client certificates. This bypass enables an attacker to intercept and spoof the collector connection, potentially leading to the unauthorized reading or alteration of sensitive log telemetry.

    Source: redhat_csaf, suse_csaf, OSV (Open Source Vulnerabilities), cvelistv5, NVD (NIST), GitHub Security Advisories, Microsoft Security Update Guide

    Affected products

    The following versions are affected. Older releases of the same product line are also vulnerable unless stated otherwise.

    Affected products
    Affected versionsFixed in
    open-telemetryopentelemetry-go
    • < 0.21.0
    • 0.21.0
    gogo.opentelemetry.io/otel/exporters/otlp/otlplog/otlploggrpc
    • —
    • —

    Vendors and products

    Weakness classes (CWE)

    • CWE-295Improper Certificate Validation

      Base

      The product does not validate, or incorrectly validates, a certificate.

      Entry at MITRE CWE-295

    • CWE-923Improper Restriction of Communication Channel to Intended Endpoints

      Class

      The product establishes a communication channel to (or from) an endpoint for privileged or protected operations, but it does not properly ensure that it is communicating with the correct endpoint.

      Entry at MITRE CWE-923

    References & sources

    • github.comopen-telemetry/opentelemetry-go/security/advisories/GHSA-w34q-c…x_refsource_CONFIRM
    • github.comopen-telemetry/opentelemetry-go/commit/c65d435b43e5e6b82310e6b1…x_refsource_MISC
    • github.comopen-telemetry/opentelemetry-go/releases/tag/exporters/otlp/otl…x_refsource_MISC
    • NVD (NIST)vuln/detail/CVE-2026-81871advisory
    • github.comopen-telemetry/opentelemetry-gopackage

    Changes to this CVE

    Who changed this CVE and when: NVD (analysis, affected products, CVSS), the CVE publisher (CNA) and additional providers such as CISA (ADP).

    1. Record modifiedCISA ADP

      CISA assessment (SSVC): exploitation: none known, automatable: no

      Show the original change
      Individual changes of this event as published by NVD
      TypeActionBeforeAfter
      SSVC assessmentadded
      —
      {"id":"CVE-2026-81871","role":"CISA Coordinator","options":[{"exploitation":"none"},{"automatable":"no"},{"technicalImpact":"partial"}],"version":"2.0.3","timestamp":"2026-09-17T17:10:34.419383Z"}

      Source identifier: 134c704f-9b21-4f2e-91b3-4a467353bcc0

    2. ReceivedGitHub

      CVSS V4.0: AV:N/AC:L/AT:P/PR:N/UI:N/VC:L/VI:L/VA:N/SC:N/SI:N/SA:N

      Weakness type: CWE-295, CWE-923

      Description added or changed

      Show 8 original changes
      Individual changes of this event as published by NVD
      TypeActionBeforeAfter
      Descriptionadded
      —
      OpenTelemetry-Go is the Go implementation of OpenTelemetry. Prior to version 0.21.0, the exporters/otlp/otlplog/otlploggrpc package loads OTEL_EXPORTER_OTLP_LOGS_CERTIFICATE, OTEL_EXPORTER_OTLP_CERTIFICATE, and related client certificate environment variables through loadEnvTLS into cfg.tlsCfg, but newGRPCDialOptions does not apply cfg.tlsCfg when creating gRPC transport credentials. The environment-only TLS path instead uses credentials.NewTLS with system roots and no configured client certificate, bypassing intended private CA pinning and mutual TLS unless the application also supplies WithTLSCredentials. A network attacker able to intercept or spoof the collector connection with a system-trusted certificate can read or alter log telemetry. This issue is fixed in version 0.21.0.
      CVSSadded
      —
      AV:N/AC:L/AT:P/PR:N/UI:N/VC:L/VI:L/VA:N/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
      Weakness type (CWE)added
      —
      CWE-295
      Weakness type (CWE)added
      —
      CWE-923
      Affected versions (publisher)added
      —
      New affected value received. <a href="https://github.com/CVEProject/cvelistV5/blob/main/cves/2026/81xxx/CVE-2026-81871.json">CVE-2026-81871</a>
      Referenceadded
      —
      https://github.com/open-telemetry/opentelemetry-go/commit/c65d435b43e5e6b82310e6b18dd4cdcb8ac63a0c
      Referenceadded
      —
      https://github.com/open-telemetry/opentelemetry-go/releases/tag/exporters/otlp/otlplog/otlploggrpc/v0.21.0
      Referenceadded
      —
      https://github.com/open-telemetry/opentelemetry-go/security/advisories/GHSA-w34q-cm8f-9c5x

      Source identifier: security-advisories@github.com

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