CVE-2026-88340: YARA Use-After-Free Vulnerability

CVE-2026-88340 Overview

CVE-2026-88340 is an invalid pointer release vulnerability in YARA 4.5.8, the pattern-matching engine widely used for malware research and identification. The flaw occurs during deserialization of compiled .yrc rule files. YARA fails to properly validate external-variable pointers embedded in serialized rules. An attacker who supplies a crafted .yrc file can trigger an invalid free in yr_rules_destroy() or wild pointer access in yr_object_create(), producing memory corruption and application crashes.

Critical Impact
Loading a malicious compiled YARA rule file causes memory corruption and denial of service in any pipeline that consumes untrusted .yrc artifacts, including automated malware analysis platforms.

Affected Products

YARA 4.5.8
Applications and sandboxes that load third-party compiled .yrc rule files
Malware analysis pipelines embedding libyara for rule deserialization

Discovery Timeline

2026-09-22 - CVE-2026-88340 published to NVD
2026-09-22 - Last updated in NVD database

Technical Details for CVE-2026-88340

Vulnerability Analysis

YARA supports serializing compiled rules to .yrc files through yr_rules_save() and reloading them via yr_rules_load(). Deserialization reconstructs internal rule structures, including external variables and their associated objects. The vulnerable code path trusts pointer fields recovered from the serialized stream without validating that they reference initialized memory owned by the current process.

When a crafted .yrc file contains malformed external-variable metadata, the deserializer instantiates rule objects that reference uninitialized or attacker-influenced pointer values. Subsequent teardown through yr_rules_destroy() calls free() on those pointers, producing an invalid free. Along a parallel path, yr_object_create() dereferences the same wild pointers, resulting in memory corruption before cleanup even runs.

Root Cause

The root cause is insufficient validation of external-variable pointer fields during rule deserialization. Compiled .yrc files are treated as trusted binary blobs, but YARA does not verify that pointer offsets and object references have been reconstructed against safe, freshly allocated memory. This is a deserialization defect with memory-corruption consequences rather than a parser bug in the rule language itself.

Attack Vector

Exploitation requires an attacker to deliver a malicious .yrc file to a system that calls yr_rules_load() or the equivalent CLI path yara -C. Automated malware analysis platforms, threat intelligence exchanges, and shared detection repositories are natural distribution channels. Successful exploitation crashes the YARA process and may corrupt heap metadata prior to termination. Details and the fix are tracked in YARA Issue #2239 and Pull Request #2244.

No public proof-of-concept exploitation code has been verified for this advisory. Refer to the upstream patch diff for the exact validation logic added to the deserializer.

Detection Methods for CVE-2026-88340

Indicators of Compromise

Unexpected crashes or SIGSEGV in processes linking libyara immediately after loading a .yrc file
.yrc files received from untrusted sources or downloaded outside of an authenticated rule-distribution channel
Heap corruption diagnostics from AddressSanitizer or glibc malloc() such as free(): invalid pointer in YARA-hosting processes

Detection Strategies

Instrument YARA-consuming services with crash telemetry and forward core dumps to a central analysis pipeline
Validate the origin and integrity of .yrc files using cryptographic signatures before loading
Run YARA under sandboxed or hardened builds compiled with AddressSanitizer during triage of new rule feeds

Monitoring Recommendations

Alert on repeated abnormal terminations of malware analysis workers that ingest external rule files
Monitor filesystem paths used by rule-distribution jobs for unsigned or unexpected .yrc artifacts
Correlate YARA process crashes with the specific rule file loaded to accelerate root-cause analysis

How to Mitigate CVE-2026-88340

Immediate Actions Required

Stop loading .yrc files from any source that is not fully trusted and integrity-verified
Rebuild rules from source .yar files on the target host instead of accepting precompiled artifacts
Isolate YARA-based analysis workers so that a crash does not disrupt broader detection pipelines

Patch Information

A fix is proposed in YARA Pull Request #2244, which adds validation of external-variable pointers during deserialization. Track the upstream VirusTotal/yara repository for a tagged release that includes the merged patch and upgrade libyara in all embedding applications.

Workarounds

Compile YARA rules locally from vetted .yar sources and disable ingestion of external .yrc files
Enforce cryptographic signature verification on any .yrc distributed across teams or tenants
Run YARA consumers under least-privilege service accounts to constrain the impact of a crash or memory corruption

bash

# Configuration example: compile rules locally instead of accepting .yrc
yarac -w /trusted/rules/index.yar /var/lib/yara/compiled.yrc
sha256sum /var/lib/yara/compiled.yrc > /var/lib/yara/compiled.yrc.sha256
# Verify before load
sha256sum -c /var/lib/yara/compiled.yrc.sha256 && yara /var/lib/yara/compiled.yrc /sample