CVE-2026-43623: Stack Buffer Overflow in microtar TAR Archive Parsing

Technical summary

The vulnerability exists in the raw_to_header() function within src/microtar.c. The ustar TAR format specifies 100-byte name and linkname fields that are not guaranteed to be null-terminated. microtar uses strcpy() to copy these fields into fixed 100-byte buffers on the stack. When an attacker supplies a crafted TAR archive with non-null-terminated fields, strcpy() continues copying beyond the intended 100 bytes—potentially writing up to 355 bytes total—until it encounters a null byte in memory. This stack-based buffer overflow corrupts adjacent stack variables, return addresses, and other sensitive data. The vulnerability is triggered when any of three functions process the malicious archive: mtar_open(), mtar_find(), or mtar_read_header().

Business impact

Applications relying on microtar to parse TAR archives face both availability and integrity risks. A denial-of-service attack is straightforward—a malicious TAR file crashes the application. More critically, a sophisticated attacker with knowledge of the application's memory layout could leverage the overflow to achieve code execution, leading to data exfiltration, system compromise, or lateral movement within a network. Organizations using microtar for backup systems, container image processing, deployment pipelines, or any archive handling should treat this as urgent.

Affected systems

microtar library versions through 0.1.0 are affected. Any application that bundles or links against this library and processes TAR archives is vulnerable. This includes deployment tools, backup utilities, embedded systems, and containerized environments that rely on TAR handling. The vulnerability requires the attacker to supply a crafted TAR file—typically through a download, upload mechanism, or network transfer—making the attack vector broad for applications handling archives from untrusted sources.

Exploitability

Exploitation requires minimal skill. An attacker simply needs to craft a TAR archive with a non-null-terminated name or linkname field and deliver it to a vulnerable application. The CVSS score of 8.8 (HIGH) reflects that no special privileges or authentication is required (PR:N), the attack can be conducted over a network (AV:N), and it requires only user interaction (UI:R) in typical deployment scenarios. No system-level access, advanced reconnaissance, or race conditions are necessary.

Remediation

Upgrade microtar to a patched version that replaces strcpy() with bounds-checked alternatives such as strncpy(), memcpy() with explicit length validation, or safer standard library functions. Verify with the microtar project's advisory or repository for the specific version that addresses this flaw. As an interim control, isolate or restrict processing of TAR archives from untrusted sources, implement input validation at the application boundary, and run archive processing in sandboxed or low-privilege contexts to limit the impact of exploitation.

Patch guidance

Check the official microtar repository and security advisories for the patched version that supersedes 0.1.0. Apply the patch as soon as feasible, prioritizing systems that process TAR archives in automated workflows or from external sources. Verify the patch by reviewing the git commit or release notes to confirm that strcpy() calls in raw_to_header() have been replaced with length-bounded string operations. Test patched versions against your own TAR processing workflows before full deployment.

Detection guidance

Monitor for crashes or segmentation faults in applications using microtar when processing TAR files, particularly if crash frequency increases. Implement filesystem monitoring to detect sudden creation of crash dumps or core files. At the network level, look for abnormal TAR archive characteristics: unusually large field lengths, missing null terminators in header fields, or archives that trigger repeated errors during parsing. Application-level logging should capture any error conditions thrown by archive parsing functions, which may indicate exploitation attempts.

Why prioritize this

The combination of a high CVSS score (8.8), network-accessible attack vector, and minimal attacker prerequisites makes this a Priority 1 vulnerability for any organization using microtar. The stack buffer overflow can lead to both immediate denial of service and potential code execution, depending on the application's memory layout and exploit sophistication. Organizations should patch or implement controls within days, not weeks.

Risk score, explained

CVSS 8.8 (HIGH) reflects: network-accessible attack vector (AV:N), low attack complexity (AC:L), no authentication or privilege escalation needed (PR:N/UI:R), and high impact across confidentiality, integrity, and availability (C:H/I:H/A:H). The score does not assume exploitation leading to code execution in all cases, but the stack overflow nature and potential for memory corruption justify the HIGH severity. Organizations with strict risk tolerance should treat this as CRITICAL if microtar is used in production for untrusted archive processing.

Frequently asked questions