CVE-2026-38638 Overview
CVE-2026-38638 is a denial-of-service vulnerability in the with_argv function located in /unistd/mod.rs of relibc, the C standard library implementation used by the Redox operating system. The flaw is present in commit 61f42d. Attackers can trigger the condition remotely by supplying crafted input, causing uncontrolled resource consumption ([CWE-400]) and disrupting availability of applications linked against relibc. The issue requires no authentication and no user interaction, and it affects availability only.
Critical Impact
Remote unauthenticated attackers can crash processes that rely on relibc argument handling, degrading service availability across affected Redox OS deployments.
Affected Products
- relibc (Redox OS C library) at commit 61f42d
- Redox OS builds that include the vulnerable relibc revision
- Downstream applications linked against the affected relibc version
Discovery Timeline
- 2026-08-28 - CVE-2026-38638 published to NVD
- 2026-08-28 - Last updated in NVD database
Technical Details for CVE-2026-38638
Vulnerability Analysis
The vulnerability resides in the with_argv helper inside /unistd/mod.rs, which is responsible for processing argument vectors during process-related unistd operations. When the function receives crafted input, it fails to properly bound resource usage, leading to uncontrolled consumption of process resources. The result is a denial-of-service condition that terminates or hangs the affected process. Because relibc underpins user-space applications on Redox OS, the impact extends to any binary that invokes the affected code path with attacker-influenced arguments.
The issue is tracked upstream in the Redox project as issue and work item #261, with a corresponding fix delivered in merge request #989. A public proof-of-concept is available in a third-party repository, demonstrating that the crash is deterministic given the crafted input.
Root Cause
The root cause is uncontrolled resource consumption ([CWE-400]) within with_argv. The function does not enforce sufficient validation or bounds when handling the argument vector supplied to it. Crafted input drives the function into a resource-exhausting execution path, and the process cannot recover, producing a DoS outcome. Confidentiality and integrity are not affected.
Attack Vector
Exploitation occurs over the network attack surface when a vulnerable relibc-linked service processes attacker-supplied argument data. The attacker does not need credentials or user interaction. Delivery mechanics depend on the specific application: any interface that forwards untrusted input into with_argv argument construction can serve as the entry point. Refer to the GitHub PoC for CVE-2026-38638 and Redox Issue #261 for reproduction details.
Detection Methods for CVE-2026-38638
Indicators of Compromise
- Repeated abnormal terminations or hangs of relibc-linked processes on Redox OS hosts.
- Spikes in CPU or memory consumption for processes invoking unistd argument handling paths.
- Crash traces or core dumps referencing with_argv in /unistd/mod.rs.
Detection Strategies
- Track relibc version and commit metadata across Redox OS builds and alert when commit 61f42d or earlier vulnerable revisions are present.
- Correlate process crash events with inbound network requests carrying oversized or malformed argument payloads.
- Use fuzzing or replay of the public proof-of-concept in a controlled environment to validate exposure.
Monitoring Recommendations
- Monitor service uptime and restart counters for Redox OS workloads that expose network-reachable interfaces.
- Instrument syscalls and resource-usage counters around unistd operations to catch resource-exhaustion patterns.
- Forward host telemetry, crash logs, and network metadata into a centralized analytics pipeline for correlation.
How to Mitigate CVE-2026-38638
Immediate Actions Required
- Inventory Redox OS systems and identify binaries linked against relibc commit 61f42d or earlier.
- Apply the upstream fix from Redox Merge Request #989 and rebuild affected applications.
- Restrict network exposure of Redox OS services that process untrusted argument input until patched.
Patch Information
The fix is delivered through Redox Merge Request #989, which resolves Redox Issue #261. Rebuild relibc from a revision that includes the merge request and redeploy dependent binaries. Verify the patched build against the GitHub PoC for CVE-2026-38638 to confirm the crash no longer reproduces.
Workarounds
- Place vulnerable services behind an input-validating proxy that caps argument sizes and rejects malformed payloads.
- Apply strict rate limiting and connection quotas on network interfaces feeding relibc-linked processes.
- Enable process supervision with automatic restart and resource cgroups to contain resource-exhaustion attempts.
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
