Is CVE-2026-27820 in the CISA KEV catalog?

No. CVE-2026-27820 is not currently on the CISA Known Exploited Vulnerabilities list.

What is the CVSS severity of CVE-2026-27820?

CVE-2026-27820 has a CVSS v3 base score of 9.8 (Low).

What is the EPSS score for CVE-2026-27820?

CVE-2026-27820 has an EPSS score of 0.56% (42th percentile), estimating the probability of exploitation in the next 30 days.

How do I fix CVE-2026-27820?

Upgrade ruby4 on rhel 8 to 0-main@aarch64 or later. Fixes are available for 2 affected products.

CVE & CISA-KEV Catalog

CVE-2026-27820

LOW

9.8

CVSS v3

NVD

Description

zlib is a Ruby interface for the zlib compression/decompression library. Versions 3.0.0 and below, 3.1.0, 3.1.1, 3.2.0 and 3.2.1 contain a buffer overflow vulnerability in the Zlib::GzipReader. The zstream_buffer_ungets 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. This issue has been fixed in versions 3.0.1, 3.1.2 and 3.2.3.

CWE-120Classic Buffer Overflow CWE-131

How to fix

Remediation Available

ruby4Red Hat / RHEL

Fixed in:0-main@aarch64RHSA-2026:8838

Fixed in:0-main@srcRHSA-2026:8838

Fixed in:0-main@x86_64RHSA-2026:8838

Fixed in:0-main@noarchRHSA-2026:8838

ruby4Rocky

Fixed in:0-main@aarch64RHSA-2026:8838

Fixed in:0-main@srcRHSA-2026:8838

Fixed in:0-main@x86_64RHSA-2026:8838

Fixed in:0-main@noarchRHSA-2026:8838

Remediation is compiled from vendor and distribution security advisories. Always confirm against the linked source for your exact version and platform.

CVSS v3 Vector

Exploitability

Attack VectorNetwork

Attack ComplexityLow

Privileges RequiredNone

User InteractionNone

ScopeUnchanged

Impact

ConfidentialityHigh

IntegrityHigh

AvailabilityHigh

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

Exploit Intelligence

0.56%probability of exploitation in 30 days

42ndpercentile

Moderate risk: more likely to be exploited than 42% of all known CVEs.

References

Vendor Advisory1

github.com

Other references1

hackerone.com

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This product uses NVD data but is not endorsed or certified by the NVD. EPSS scores courtesy of FIRST.org (https://www.first.org/epss). Source: CISA KEV Catalog. Data as of 2026-05-21.