CVE-2026-21996 Overview
CVE-2026-21996 is a denial-of-service vulnerability in the dtrace process on Oracle Linux. An unprivileged local attacker can reliably crash dtrace by supplying a malicious Executable and Linkable Format (ELF) binary. The flaw is an integer divide-by-zero condition in the Pbuild_file_symtab() function, classified under CWE-369. The vulnerability affects Oracle Linux 8, 9, and 10. It does not impact confidentiality or integrity but produces a high availability impact on the affected tracing process.
Critical Impact
A local, low-privileged user can crash the dtrace process on demand, disrupting kernel tracing, observability, and dependent diagnostic workflows.
Affected Products
- Oracle Linux 8
- Oracle Linux 9
- Oracle Linux 10
Discovery Timeline
- 2026-05-01 - CVE-2026-21996 published to NVD
- 2026-05-05 - Last updated in NVD database
Technical Details for CVE-2026-21996
Vulnerability Analysis
The vulnerability resides in Pbuild_file_symtab(), a routine in the DTrace user-space process responsible for building a symbol table from an ELF binary. When parsing attacker-controlled ELF metadata, the function performs an integer division using a value derived from section header fields without validating that the divisor is non-zero. Supplying an ELF file with crafted section header sizes causes the divisor to evaluate to zero, raising a hardware exception that terminates the dtrace process.
Because dtrace is invoked to inspect ELF binaries during tracing operations, an unprivileged user only needs to point the tool at a malicious file or stage a binary that will be inspected. The attack requires local access and low privileges, and no user interaction is required beyond delivering the ELF input.
Root Cause
The root cause is missing input validation on ELF section header values used as a divisor inside Pbuild_file_symtab(). The parser trusts fields such as section entry size without verifying they are greater than zero before performing division. This matches the CWE-369: Divide By Zero weakness pattern.
Attack Vector
Exploitation is local. An attacker with shell access creates a malformed ELF binary whose section header table contains a zero-valued field used as a divisor. When dtrace parses the binary through Pbuild_file_symtab(), the division aborts the process. Repeated triggering provides a reliable denial of service against tracing infrastructure. Refer to the Oracle Linux advisory for CVE-2026-21996 for vendor-confirmed details.
Detection Methods for CVE-2026-21996
Indicators of Compromise
- Repeated abnormal terminations of the dtrace process with SIGFPE (signal 8) recorded in audit or dmesg output.
- Presence of unexpected or unsigned ELF binaries in user-writable directories that are subsequently passed to dtrace.
- Core dumps or systemd-coredump entries naming dtrace as the failing executable.
Detection Strategies
- Monitor process exit codes and signals for dtrace invocations and alert on SIGFPE terminations.
- Correlate ELF file creation events by non-privileged users with subsequent dtrace execution against those paths.
- Inspect ELF section headers for zero-valued sh_entsize fields when dtrace is part of automated workflows.
Monitoring Recommendations
- Enable auditd rules covering execve of /usr/sbin/dtrace and capture command-line arguments referencing user-controlled paths.
- Forward kernel and coredump telemetry to a centralized logging platform for trend analysis.
- Track frequency of dtrace crashes per host and alert on anomalous spikes that may indicate abuse.
How to Mitigate CVE-2026-21996
Immediate Actions Required
- Apply Oracle Linux package updates for dtrace once available through yum or dnf on Oracle Linux 8, 9, and 10.
- Restrict execution of dtrace to administrative users via sudo policies until patches are deployed.
- Inventory environments where dtrace is invoked against user-supplied ELF files and isolate those workflows.
Patch Information
Oracle distributes fixes through the Oracle Linux errata channel. Consult the Oracle Linux CVE-2026-21996 advisory for the specific package versions and errata identifiers, then update with sudo dnf update dtrace once the fixed package is published for your release.
Workarounds
- Limit dtrace execution to trusted operators by tightening file permissions and sudoers entries.
- Avoid running dtrace against ELF binaries staged by untrusted local accounts.
- Use mandatory access control through SELinux to constrain which users can invoke tracing utilities.
# Restrict dtrace to the wheel group until a patch is applied
sudo chown root:wheel /usr/sbin/dtrace
sudo chmod 750 /usr/sbin/dtrace
# Verify installed package version after patching
rpm -q dtrace
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
