CVE-2018-8778

CVE-2018-8778 is a high-severity vulnerability in Ruby-lang Ruby with a CVSS 3.x base score of 7.5. It is not currently listed as actively exploited by CISA, and its EPSS exploit-prediction score is low. The underlying weakness is classified as CWE-134.

Key facts

• Severity: High (CVSS 3.x base score 7.5)
• CVSS v2: 5.0
• EPSS exploit prediction: 8% (94th percentile)
• Actively exploited: Not listed in CISA KEV
• Weakness: CWE-134
• Affected product: Ruby-lang Ruby
• Published: 2018-04-03
• Last modified: 2026-06-17

Description

In Ruby before 2.2.10, 2.3.x before 2.3.7, 2.4.x before 2.4.4, 2.5.x before 2.5.1, and 2.6.0-preview1, an attacker controlling the unpacking format (similar to format string vulnerabilities) can trigger a buffer under-read in the String#unpack method, resulting in a massive and controlled information disclosure.

Frequently asked questions

What is CVE-2018-8778?

In Ruby before 2.2.10, 2.3.x before 2.3.7, 2.4.x before 2.4.4, 2.5.x before 2.5.1, and 2.6.0-preview1, an attacker controlling the unpacking format (similar to format string vulnerabilities) can trigger a buffer under-read in the String#unpack method, resulting in a massive and controlled information disclosure.

How severe is CVE-2018-8778?

CVE-2018-8778 has a CVSS 3.x base score of 7.5, rated high severity. It is exploitable over network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is high, integrity none, and availability none.

Is CVE-2018-8778 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 8% (94th percentile), an estimate of the probability of exploitation in the next 30 days.

What products are affected by CVE-2018-8778?

CVE-2018-8778 primarily affects Ruby-lang Ruby. In total, 13 product configurations (CPEs) are listed as vulnerable; see the affected-products list for the exact versions.

How do I fix CVE-2018-8778?

Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its high severity, prioritise patching exposed systems.

When was CVE-2018-8778 published?

CVE-2018-8778 was published on 2018-04-03 and last updated on 2026-06-17.

References

• http://lists.opensuse.org/opensuse-security-announce/2019-07/msg00036.html
• http://www.securityfocus.com/bid/103693
• http://www.securitytracker.com/id/1042004
• https://access.redhat.com/errata/RHSA-2018:3729
• https://access.redhat.com/errata/RHSA-2018:3730
• https://access.redhat.com/errata/RHSA-2018:3731
• https://access.redhat.com/errata/RHSA-2019:2028
• https://lists.debian.org/debian-lts-announce/2018/04/msg00023.html
• https://lists.debian.org/debian-lts-announce/2018/04/msg00024.html
• https://lists.debian.org/debian-lts-announce/2018/07/msg00012.html
• https://usn.ubuntu.com/3626-1/
• https://www.debian.org/security/2018/dsa-4259
• https://www.ruby-lang.org/en/news/2018/03/28/buffer-under-read-unpack-cve-2018-8778/
• https://www.ruby-lang.org/en/news/2018/03/28/ruby-2-2-10-released/
• https://www.ruby-lang.org/en/news/2018/03/28/ruby-2-3-7-released/
• https://www.ruby-lang.org/en/news/2018/03/28/ruby-2-4-4-released/
• https://www.ruby-lang.org/en/news/2018/03/28/ruby-2-5-1-released/

Affected products (13)

• cpe:2.3:a:ruby-lang:ruby:*:*:*:*:*:*:*:*
• cpe:2.3:a:ruby-lang:ruby:2.6.0:preview1:*:*:*:*:*:*
• cpe:2.3:o:canonical:ubuntu_linux:14.04:*:*:*:lts:*:*:*
• cpe:2.3:o:canonical:ubuntu_linux:16.04:*:*:*:lts:*:*:*
• cpe:2.3:o:canonical:ubuntu_linux:17.10:*:*:*:*:*:*:*
• cpe:2.3:o:debian:debian_linux:7.0:*:*:*:*:*:*:*
• cpe:2.3:o:debian:debian_linux:8.0:*:*:*:*:*:*:*
• cpe:2.3:o:debian:debian_linux:9.0:*:*:*:*:*:*:*
• cpe:2.3:o:redhat:enterprise_linux:6.0:*:*:*:*:*:*:*
• cpe:2.3:o:redhat:enterprise_linux:7.0:*:*:*:*:*:*:*
• cpe:2.3:o:redhat:enterprise_linux:7.4:*:*:*:*:*:*:*
• cpe:2.3:o:redhat:enterprise_linux:7.5:*:*:*:*:*:*:*
• cpe:2.3:o:redhat:enterprise_linux:7.6:*:*:*:*:*:*:*

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• CVE-2011-1568 — Critical (CVSS 10.0): Format string vulnerability in the logText function in shmemmgr9.dll in IGSSdataServer.exe 9.00.00.11074, and…
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