CVE-2018-25032 is a high-severity (CVSS 7.5) Out-of-bounds Write vulnerability in nokogiri. 2 public exploit references exist, so weaponization risk is real. A fix is available for nokogiri — see the affected versions and patch details below.
Nokogiri affected by zlib's Out-of-bounds Write vulnerability
Exploitation Status
Proof-of-concept exploit code exists
- CISA’s SSVC triage found public proof-of-concept exploit code for this CVE, though no confirmed active exploitation.
- CISA assesses this as automatable — exploitation doesn’t require manual, per-target effort, which raises the odds of mass scanning and opportunistic attacks.
Exploitation and automatability from CISA’s SSVC triage for CVE-2018-25032.
EPSS Exploitation Probability
EPSS (Exploit Prediction Scoring System) is a daily probability model maintained by FIRST.org. It estimates the likelihood a CVE will be exploited in production environments within the next 30 days, derived from real-world threat intelligence signals.
How urgent is this, really
CVE-2018-25032 plotted by exploitation likelihood (EPSS) against impact (CVSS). The shaded corner — EPSS 50%+ and CVSS 7.0+ — is where this CVE sits: patch-first territory.
Where this sits among everything scored
Of 377,636 CVEs with a current EPSS score, this one falls in the 50–90% band (highlighted). Real counts from FIRST.org, not a sample — log-scaled since the landscape is heavily right-skewed.
Real-World Exposure
nokogiriReal-time download stats are indexed for npm and PyPI packages. This vulnerability affects RubyGems packages — download data is not available via public APIs for these ecosystems.
Description
zlib before 1.2.12 allows memory corruption when deflating (i.e., when compressing) if the input has many distant matches.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 💎RubyGems | nokogiri | all versions | 1.13.4bundle update nokogiri --conservative |
Research use only. For defensive security, authorized penetration testing, and academic research only. Never execute exploit code against systems without explicit written authorization.
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for nokogiri, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update nokogiri to 1.13.4 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2018-25032 is resolved across your whole dependency graph.
Workarounds
If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.
How O3 protects you
O3 Security's impact-aware SCA analyses which vulnerable code paths your application actually calls, so a match like CVE-2018-25032 can be triaged on real exposure rather than presence alone.
Tailored to CVE-2018-25032. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.
Fixing This On Your OS
If you run this on a Linux distribution, patch through your package manager against the distro's own security advisory below — it tracks the exact backported fix for your release, which can ship on a different timeline (and sometimes a different severity) than the upstream project.
This bug was introduced in zlib v1.2.2.2 through zlib v1.2.11, with the addition of the Z_FIXED option, which forces the use of fixed Huffman codes, rather than dynamic Huffman codes, allowing for a simpler decoder for special applications. This bug is difficult to trigger, as Z_FIXED is usually only used in special…
| Product | Fixed in | Advisory |
|---|---|---|
| Red Hat Enterprise Linux 6 Extended Lifecycle Support | zlib-0:1.2.3-31.el6_10 | RHSA-2022:2214 |
| Red Hat Enterprise Linux 7 | zlib-0:1.2.7-20.el7_9 | RHSA-2022:2213 |
| Red Hat Enterprise Linux 7.4 Advanced Update Support | zlib-0:1.2.7-17.el7_4.1 | RHSA-2023:0976 |
| Red Hat Enterprise Linux 7.6 Advanced Update Support | zlib-0:1.2.7-18.el7_6.1 | RHSA-2023:0975 |
| Red Hat Enterprise Linux 7.7 Advanced Update Support | zlib-0:1.2.7-18.el7_7.1 | RHSA-2023:0943 |
| Red Hat Enterprise Linux 8 | mingw-zlib-0:1.2.8-10.el8 | RHSA-2022:7813 |
| Red Hat Enterprise Linux 8 | zlib-0:1.2.11-18.el8_5 | RHSA-2022:1642 |
| Red Hat Enterprise Linux 8 | rsync-0:3.1.3-14.el8_6.2 | RHSA-2022:2201 |
Frequently Asked Questions
Is CVE-2018-25032 in your dependencies?
O3 Security finds CVE-2018-25032 across RubyGems dependencies, including transitive ones, and its impact-aware SCA ranks findings by whether your code actually calls the vulnerable path.