fflate through 0.8.2 is vulnerable to denial of service via an infinite loop in unzipSync(). A crafted ZIP archive with a central directory entry declaring compressed_size=0xFFFFFFFF (ZIP64 sentinel) but missing the required ZIP64 extra field tag 0x0001 causes z64e() to loop indefinitely due to out-of-bounds reads returning undefined, which coerces to 0, keeping the loop condition permanently true.
CVE-2026-45820
MEDIUMPre-NVD 6.66.6—Trending — 4 sources updated this week
EchelonGraph scoreMEDIUM confidence
This medium-severity CVE scores 6.6 under a secondary CVSS source (NVD's own analysis pending). EPSS exploit probability: 0.3%, top 83% of all CVEs by exploit prediction. GitHub Security Advisory data not yet ingested — confidence will rise once GHSA publishes (typical lag: hours to days for open-source ecosystem CVEs; never for infrastructure-only CVEs).
Triggered by: NVD CVSS baseline
Sources: epss, secondary
6.6
EchelonGraph verdictMonitorLow exploitation likelihood right now — keep watching.
- Lower severity and no public exploit yet
CISA-KEV: Not listedEPSS: 0%CVSS: 6.6Exploit: NoneExposed: 0
No vendor fix yet — apply a workaround or compensating control (WAF / firewall / segmentation) and watch for a patch.
- CVSS v3
- 6.6
- EG Score
- 6.6(medium)
- EPSS
- 17.1%
- KEV
- Not listed
Published
July 22, 2026
Last Modified
July 22, 2026
Advisory Details (1)
Auto-updated Jul 22, 2026No patch confirmed yet.
generic
fflate/src/index.ts at f7873560ad229c22c4b23b06c6a3806ffde77569 · 101arrowz/fflate · GitHub
https://github.com/101arrowz/fflate/blob/f7873560ad229c22c4b23b06c6a3806ffde77569/src/index.ts#L2714Vendor Advisories for CVE-2026-45820(1)
These vendors published their own advisory mentioning this CVE — often with vendor-specific remediation steps + affected product lists not in NVD.
Weakness Classification(2)
MITRE Common Weakness Enumeration — the root-cause categories this CVE belongs to.
Data Freshness Timeline
(refreshed 9× in last 7d / 9× in last 30d)
Each row is a source pipeline that fetched or updated this CVE on that date, with what changed. For example, "NVD update" means NVD published or revised its analysis for this CVE; "MITRE cvelistV5" means we ingested or refreshed it from the CNA feed. Most recent first.
- 2026-07-22 15:01 UTCEG score recompute
- 2026-07-22 15:00 UTCGHSA enrichment
- 2026-07-22 14:08 UTCEPSS rescore
- 2026-07-22 13:21 UTCEG score recompute
- 2026-07-22 13:21 UTCGHSA enrichment
- 2026-07-22 09:32 UTCEG score recompute
- 2026-07-22 09:32 UTCGHSA enrichment
- 2026-07-22 07:29 UTCEG score recompute
- 2026-07-22 07:28 UTCMITRE cvelistV5first tracked
Frequently asked(5)
What is CVE-2026-45820?
CVE-2026-45820 is a medium vulnerability published on July 22, 2026. fflate through 0.8.2 is vulnerable to denial of service via an infinite loop in unzipSync(). A crafted ZIP archive with a central directory entry declaring compressed_size=0xFFFFFFFF (ZIP64 sentinel) but missing the required ZIP64 extra field tag 0x0001 causes z64e() to loop indefinitely due to…
When was CVE-2026-45820 disclosed?
CVE-2026-45820 was first published in the National Vulnerability Database on July 22, 2026. EchelonGraph re-ingests CVE updates from NVD on a 2-hour cycle, so this page reflects the latest published state.
Is CVE-2026-45820 actively exploited?
CVE-2026-45820 is not currently on CISA's Known Exploited Vulnerabilities catalog. FIRST EPSS estimates a 17.1% percentile likelihood of exploitation in the next 30 days — higher percentiles indicate greater predicted risk.
What is the CVSS score of CVE-2026-45820?
CVE-2026-45820 has a CVSS v3 base score of 6.6 (NVD).
How do I remediate CVE-2026-45820?
Patch to the fixed version published by the affected vendor. Where vendor advisories exist for CVE-2026-45820, EchelonGraph cross-links them in the Vendor Advisories panel below — those typically contain the canonical remediation steps, fixed version numbers, and any vendor-specific mitigations.
Dependency Blast Radius
Explore the affected products and dependency analysis for CVE-2026-45820
Is Your Infrastructure Affected by CVE-2026-45820?
EchelonGraph automatically scans your cloud infrastructure and maps CVE exposure using blast radius analysis.