# CVE-2026-109380: modern-tar 0.3.5 through 0.8.5 Memory Exhaustion via Malformed Octal Size Field

> Attackers can cause memory exhaustion and denial of service in modern-tar by supplying a crafted archive with malformed octal size fields.

- **Severity:** High 8.7 (`CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** No
- **Published:** 12 Oct 2026
- **Updated:** 13 Oct 2026
- **Also known as:** GHSA-m6wr-6wgx-82mm

## What is CVE-2026-109380?

CVE-2026-109380 is a high-severity denial of service vulnerability in ayuhito modern-tar, published on 12 Oct 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

modern-tar 0.3.5 through 0.8.5 contains a memory exhaustion vulnerability that allows attackers to produce negative entry sizes via non-octal bytes parsed by readOctal(). Attackers can supply a crafted, optionally gzip-compressed, archive to unpackTar() that buffers chunks indefinitely, exhausting process memory and suppressing later entries.

Weakness: CWE-1284 (Improper Validation of Specified Quantity in Input)

## Which versions are affected by CVE-2026-109380?


## How do I fix CVE-2026-109380?

No fix has been published for CVE-2026-109380 yet. Limit exposure of the affected software until one is available.

## Is CVE-2026-109380 being exploited?

There is no known exploitation of CVE-2026-109380 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-109380 and fix it if it is affected.

What it is: CVE-2026-109380 is a high-severity denial of service vulnerability in ayuhito modern-tar, published on 12 Oct 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2026-109380 in the wild and no public exploit code.

Affected product: ayuhito modern-tar. No package-level version data is available, so check the vendor advisory linked from the reference page.

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-109380/ (Markdown: https://insights.sbomify.com/CVE-2026-109380/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-109380
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-109380
- OSV: https://osv.dev/vulnerability/CVE-2026-109380

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-109380/
Summaries are generated and may contain mistakes; the official description above is the record.