CVE-2018-1000120 — curl
CRITICALCVE-2018-1000120 is a critical-severity (CVSS 9.8) Out-of-bounds Write vulnerability in curl. EPSS puts its 30-day exploitation probability at 11.6% (96th percentile). The records list no fixed version yet; check the vendor advisory below and apply the mitigations in the meantime.
curl FTP path confusion leads to NIL byte out of bounds write
EPSS Exploitation Probability
Probability of exploitation in the next 30 days, from FIRST.org EPSS.
How urgent is this, really
Where this sits among everything scored
Real-World Exposure
curlReal-time download stats are indexed for npm and PyPI packages. This vulnerability affects NuGet packages — download data is not available via public APIs for these ecosystems.
Description
curl can be coerced into writing a zero byte out of bounds.
This bug can trigger when curl is told to work on an FTP URL, with the setting to only issue a single CWD command (--ftp-method singlecwd or the libcurl alternative CURLOPT_FTP_FILEMETHOD).
curl then URL-decodes the given path, calls strlen() on the result and deducts the length of the file name part to find the end of the directory within the buffer. It then writes a zero byte on that index, in a buffer allocated on the heap.
If the directory part of the URL contains a %00 sequence, the directory length might end up shorter than the file name path, making the calculation size_t index = directory_len - filepart_len end up with a huge index variable for where the zero byte gets stored: heap_buffer[index] = 0. On several architectures that huge index will wrap and work as a negative value, thus overwriting memory before the intended heap buffer.
By using different file part lengths and putting the string %00 in different places in the URL, an attacker that can control what paths a curl-using application uses can write that zero byte on different indexes.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| .NETNuGet | curl | ≥ 7.12.3 | No fix |
Affected Products
ubuntu linuxcanonicaldebian linuxdebiancurlhaxxcommunications webrtc session controlleroracleenterprise manager ops centeroraclepeoplesoft enterprise peopletoolsoracleDetection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for curl, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Remediation status
The records we use list no patched version of curl for CVE-2018-1000120. Check the maintainer's advisory, and where your build allows, override or pin the dependency away from the vulnerable range.
Mitigate without a patch
Stop feeding it untrusted input: reject or quarantine files and payloads from unverified sources until you can upgrade, restrict accepted formats to the ones you actually need, and run the parsing or decoding step in a least-privileged sandbox or short-lived worker so a crash or corrupted read cannot reach the rest of the process.
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.
Preventing application from using non-default CURLOPT_FTP_FILEMETHOD will avoid triggering the vulnerable code.Source: Red Hat security advisory for CVE-2018-1000120 (CC BY 4.0)
| Product | Fixed in | Advisory |
|---|---|---|
| JBoss Core Services Apache HTTP Server 2.4.29 SP2 | jbcs-httpd24-curl | RHSA-2019:1543 |
| Red Hat Enterprise Linux 7 | curl-0:7.29.0-51.el7 | RHSA-2018:3157 |
| Red Hat Enterprise Linux 7.4 Advanced Update Support | curl-0:7.29.0-42.el7_4.2 | RHSA-2020:0594 |
| Red Hat Enterprise Linux 7.5 Extended Update Support | curl-0:7.29.0-46.el7_5.1 | RHSA-2020:0544 |
| Red Hat Software Collections for Red Hat Enterprise Linux 6 | httpd24-curl-0:7.61.1-1.el6 | RHSA-2018:3558 |
Frequently Asked Questions
Is CVE-2018-1000120 in your dependencies?
Find it across NuGet, including transitive dependencies.