CVE-2026-45820: CWE-835 Loop with Unreachable Exit Condition ('Infinite Loop') in 101arrowz fflate
fflate versions 0.4.5 through 0.8.0 contain a vulnerability that allows denial of service via an infinite loop in the unzipSync() function. This occurs when processing a crafted ZIP archive with a central directory entry that declares a compressed size of 0xFFFFFFFF but lacks the required ZIP64 extra field tag. The infinite loop is caused by out-of-bounds reads returning undefined, which coerces to zero and keeps the loop condition true indefinitely.
AI Analysis
Technical Summary
The fflate library up to version 0.8.0 is vulnerable to a denial of service condition triggered by an infinite loop in the unzipSync() function. The issue arises when a specially crafted ZIP archive contains a central directory entry with compressed_size set to the ZIP64 sentinel value 0xFFFFFFFF but omits the mandatory ZIP64 extra field tag 0x0001. This causes the internal function z64e() to perform out-of-bounds reads that return undefined, which coerces to zero in JavaScript, causing the loop condition to never become false and resulting in an infinite loop. This vulnerability is tracked as CVE-2026-45820 with a CVSS 4.0 base score of 6.6 (medium severity). No known exploits are reported in the wild, and no official patch or remediation level has been published.
Potential Impact
Successful exploitation results in a denial of service by causing the unzipSync() function to enter an infinite loop, potentially leading to application hang or resource exhaustion. There is no indication of code execution or data corruption. The vulnerability affects unauthenticated attackers remotely via crafted ZIP files.
Mitigation Recommendations
Patch status is not yet confirmed — check the vendor advisory for current remediation guidance. Until a fix is available, avoid processing untrusted ZIP archives with fflate versions 0.4.5, 0.5.0, 0.6.0, 0.7.0, and 0.8.0. Monitor vendor channels for updates or patches addressing this issue.
CVE-2026-45820: CWE-835 Loop with Unreachable Exit Condition ('Infinite Loop') in 101arrowz fflate
Description
fflate versions 0.4.5 through 0.8.0 contain a vulnerability that allows denial of service via an infinite loop in the unzipSync() function. This occurs when processing a crafted ZIP archive with a central directory entry that declares a compressed size of 0xFFFFFFFF but lacks the required ZIP64 extra field tag. The infinite loop is caused by out-of-bounds reads returning undefined, which coerces to zero and keeps the loop condition true indefinitely.
CVSS v4.0
Score 6.6medium
Affected software
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Weaknesses
AI-Powered Analysis
Machine-generated threat intelligence
Technical Analysis
The fflate library up to version 0.8.0 is vulnerable to a denial of service condition triggered by an infinite loop in the unzipSync() function. The issue arises when a specially crafted ZIP archive contains a central directory entry with compressed_size set to the ZIP64 sentinel value 0xFFFFFFFF but omits the mandatory ZIP64 extra field tag 0x0001. This causes the internal function z64e() to perform out-of-bounds reads that return undefined, which coerces to zero in JavaScript, causing the loop condition to never become false and resulting in an infinite loop. This vulnerability is tracked as CVE-2026-45820 with a CVSS 4.0 base score of 6.6 (medium severity). No known exploits are reported in the wild, and no official patch or remediation level has been published.
Potential Impact
Successful exploitation results in a denial of service by causing the unzipSync() function to enter an infinite loop, potentially leading to application hang or resource exhaustion. There is no indication of code execution or data corruption. The vulnerability affects unauthenticated attackers remotely via crafted ZIP files.
Mitigation Recommendations
Patch status is not yet confirmed — check the vendor advisory for current remediation guidance. Until a fix is available, avoid processing untrusted ZIP archives with fflate versions 0.4.5, 0.5.0, 0.6.0, 0.7.0, and 0.8.0. Monitor vendor channels for updates or patches addressing this issue.
Technical Details
- Data Version
- 5.2
- Assigner Short Name
- seal
- Date Reserved
- 2026-05-13T12:03:13.544Z
- Cvss Version
- 4.0
- State
- PUBLISHED
- Remediation Level
- null
Threat ID: 6a60734d9c2644c7f89b9207
Added to database: 07/22/2026, 07:37:49 UTC
Last enriched: 07/22/2026, 07:53:07 UTC
Last updated: 07/22/2026, 07:53:07 UTC
Views: 5
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