CVE-2026-42191

Description

OpenTelemetry.Exporter.OpenTelemetryProtocol is the OTLP (OpenTelemetry Protocol) exporter implementation. From 1.8.0 to 1.15.2, the OTLP disk retry feature in OpenTelemetry.Exporter.OpenTelemetryProtocol silently fell back to Path.GetTempPath() when OTEL_DOTNET_EXPERIMENTAL_OTLP_RETRY=disk was set but OTEL_DOTNET_EXPERIMENTAL_OTLP_DISK_RETRY_DIRECTORY_PATH was not configured. The exporter stored and loaded *.blob files under fixed, signal-named subdirectories (traces, metrics, logs) beneath that shared temporary root path. On multi-user systems where the temporary directory is accessible to other local accounts, this allows an attacker to write crafted *.blob files, read *.blob files written by the application between export failures, or deposit numerous or oversized blob files, degrading retry-loop performance or consuming disk space. This vulnerability is fixed in 1.15.3.

CVSS Details

CVSS Score

6.5

Severity

MEDIUM

CVSS Vector

CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:L

Configurations (Affected Products)

No configuration data available.

OpenTelemetry.Exporter.OpenTelemetryProtocol >= 1.8.0, <= 1.15.2

PoC / Exploit Code

⚠ For Security Research Only

The following code is for security research and authorized testing only.

python

/*
 * PoC for CVE-2026-42191
 * This script demonstrates checking for the existence of the insecure
 * default retry directory in the system temp path.
 */

using System;
using System.IO;

public class CheckOTLPPoC
{
    public static void Main(string[] args)
    {
        // Simulate the vulnerable library's default path logic
        string tempPath = Path.GetTempPath();
        string[] signalDirs = { "traces", "metrics", "logs" };

        Console.WriteLine($"[+] Checking System Temp Path: {tempPath}");

        foreach (string dir in signalDirs)
        {
            string fullPath = Path.Combine(tempPath, dir);
            if (Directory.Exists(fullPath))
            {
                Console.WriteLine($"[!] Found vulnerable directory: {fullPath}");
                // Attempt to list files to demonstrate read access
                try {
                    string[] files = Directory.GetFiles(fullPath, "*.blob");
                    Console.WriteLine($"    - Found {files.Length} blob files accessible.");
                } catch (UnauthorizedAccessException) {
                    Console.WriteLine("    - Access denied (securely configured).");
                }
            }
            else
            {
                Console.WriteLine($"[-] Directory not found: {fullPath}");
            }
        }
    }
}

References

[1] CVE.org https://www.cve.org/CVERecord?id=CVE-2026-42191
[2] NVD NIST https://nvd.nist.gov/vuln/detail/CVE-2026-42191
[3] CVE Details https://www.cvedetails.com/cve/CVE-2026-42191/
[4] VulDB https://vuldb.com/cve/CVE-2026-42191
[5] https://github.com/open-telemetry/opentelemetry-dotnet/pull/7106
[6] https://github.com/open-telemetry/opentelemetry-dotnet/security/advisories/GHSA-4625-4j76-fww9

Raw JSON Data

JSON

{"cve": {"id": "CVE-2026-42191", "sourceIdentifier": "[email protected]", "published": "2026-05-12T20:16:41.000", "lastModified": "2026-05-13T18:16:44.010", "vulnStatus": "Awaiting Analysis", "cveTags": [], "descriptions": [{"lang": "en", "value": "OpenTelemetry.Exporter.OpenTelemetryProtocol is the OTLP (OpenTelemetry Protocol) exporter implementation. From 1.8.0 to 1.15.2, the OTLP disk retry feature in OpenTelemetry.Exporter.OpenTelemetryProtocol silently fell back to Path.GetTempPath() when OTEL_DOTNET_EXPERIMENTAL_OTLP_RETRY=disk was set but OTEL_DOTNET_EXPERIMENTAL_OTLP_DISK_RETRY_DIRECTORY_PATH was not configured. The exporter stored and loaded *.blob files under fixed, signal-named subdirectories (traces, metrics, logs) beneath that shared temporary root path. On multi-user systems where the temporary directory is accessible to other local accounts, this allows an attacker to write crafted *.blob files, read *.blob files written by the application between export failures, or deposit numerous or oversized blob files, degrading retry-loop performance or consuming disk space. This vulnerability is fixed in 1.15.3."}], "metrics": {"cvssMetricV31": [{"source": "[email protected]", "type": "Secondary", "cvssData": {"version": "3.1", "vectorString": "CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:L", "baseScore": 6.5, "baseSeverity": "MEDIUM", "attackVector": "LOCAL", "attackComplexity": "HIGH", "privilegesRequired": "LOW", "userInteraction": "NONE", "scope": "UNCHANGED", "confidentialityImpact": "HIGH", "integrityImpact": "HIGH", "availabilityImpact": "LOW"}, "exploitabilityScore": 1.0, "impactScore": 5.5}]}, "weaknesses": [{"source": "[email protected]", "type": "Primary", "description": [{"lang": "en", "value": "CWE-379"}]}], "references": [{"url": "https://github.com/open-telemetry/opentelemetry-dotnet/pull/7106", "source": "[email protected]"}, {"url": "https://github.com/open-telemetry/opentelemetry-dotnet/security/advisories/GHSA-4625-4j76-fww9", "source": "[email protected]"}]}}