Medium, CVSS 5.9RubyGemsPublished
Buffer Overflow in Zlib::GzipReader ungetc via large input leads to memory corruption
CVE-2026-27820 · GHSA-g857-hhfv-j68w
- Affected
- RubyGems zlib >= 3.2.0, < 3.2.3; >= 3.1.0, < 3.1.2; < 3.0.1
- Fixed in
- 3.0.13.1.23.2.3· Vendor fix available
- Issue
- Details A buffer overflow vulnerability exists in Zlib::GzipReader. The zstreambufferungets function prepends caller-provided bytes ahead of previously produced output but fails to guarantee the backing Ruby string has enough capacity before the memmove shifts the existing data. This can lead to memory corruption when the buffer length exceeds capacity. Recommended action We recommend to update the zlib gem to version 3.2.3 or later. In order to ensure compatibility with bundled version in older Ruby series, you may update as follows instead: For Ruby 3.2 users: Update to zlib 3.0.1 For Ruby 3.3 users: Update to zlib 3.1.2 You can use gem update zlib to update it. If you are using bundler, please add gem "zlib", "= 3.2.3" to your Gemfile. Affected versions zlib gem 3.2.2 or lower Credits calysteon References https://hackerone.com/reports/3467067
Recommended action: Upgrade to 3.2.3, 3.1.2 or 3.0.1 by release line, then redeploy and verify.A vendor fix does not resolve your finding until you verify it in your own systems.