---
title: "CVE-2023-38545: curl curl vulnerability"
url: https://erroneo.us/security/cve/CVE-2023-38545/
description: "CVE-2023-38545 (curl curl): This flaw makes curl overflow a heap based buffer in the SOCKS5 proxy handshake. When curl is asked to pass along the host name…"
type: vulnerability-record
section: "Security Digest"
date_published: 2023-10-18
date_modified: 2026-10-21
publisher: erroneo.us
author: erroneo.us Security Desk
cve: "CVE-2023-38545"
kev: false
cvss: 8.8
epss: 0.78689
license: All rights reserved. Quote with attribution and a link.
---

# CVE-2023-38545: curl curl vulnerability

**Signal:** High exploit likelihood. EPSS ranks it in the top 5% of all CVEs for likely exploitation in the next 30 days. (Computed from CISA KEV, EPSS and CVSS; not an editorial verdict.)

## Should you act?

- Not in CISA KEV , but CISA’s SSVC assessment records a public proof-of-concept, so attack code exists.
- EPSS 78.7% , percentile 99.6: FIRST’s model estimates a 78.7% chance of exploitation activity in the next 30 days, higher than 99.6% of all scored CVEs (very high). EPSS is a probability, not a verdict.
- Needs a user to click or open something. Phishing makes that realistic, but it is not wormable.
- Editorial verdict: Most can relax. curl SOCKS5 Heap Overflow: Hyped, but Narrow in Practice — Pre-announced as the worst curl flaw in a long time, the bug only bites when libcurl uses a SOCKS5 proxy with remote name resolution and an attacker can supply a very long hostname; take 8.4.0 or later in normal patching, and hurry only if that proxy setup applies to you.

## What it is

This flaw makes curl overflow a heap based buffer in the SOCKS5 proxy handshake. When curl is asked to pass along the host name to the SOCKS5 proxy to allow that to resolve the address instead of it getting done by curl itself, the maximum length that host name can be is 255 bytes. If the host name is detected to be longer, curl switches to local name resolving and instead passes on the resolved address only. Due to this bug, the local variable that means "let the host resolve the name" could get the wrong value during a slow SOCKS5 handshake, and contrary to the intention, copy the too long host name to the target buffer instead of copying just the resolved address there. The target buffer being a heap based buffer, and the host name coming from the URL that curl has been told to operate with.

## Affected products (CVE record)

- curl curl: 8.4.0 < 8.4.0

## Severity

- CISA-ADP CVSS 3.1: 8.8 `CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H`

## Exploitation

- CISA KEV: not listed (no confirmed in-the-wild exploitation known to CISA).
- CISA SSVC assessment: exploitation poc , automatable no , technical impact total .
- FIRST EPSS (model of 2026-10-21): 78.69% probability of exploitation activity in the next 30 days; percentile 99.6.

## Sources

- [CVE.org record CVE-2023-38545](https://www.cve.org/CVERecord?id=CVE-2023-38545)
- [NVD entry CVE-2023-38545](https://nvd.nist.gov/vuln/detail/CVE-2023-38545)
- [curl.se](https://curl.se/docs/CVE-2023-38545.html)
- [security.netapp.com](https://security.netapp.com/advisory/ntap-20231027-0009/)
- [lists.fedoraproject.org](https://lists.fedoraproject.org/archives/list/package-announce@lists.fedoraproject.org/message/OGMXNRNSJ4ETDK6FRNU3J7SABXPWCHSQ/)
- [secpod.com](https://www.secpod.com/blog/high-severity-heap-buffer-overflow-vulnerability/)
- [support.apple.com](https://support.apple.com/kb/HT214036)
- [support.apple.com](https://support.apple.com/kb/HT214063)
- [support.apple.com](https://support.apple.com/kb/HT214057)
- [support.apple.com](https://support.apple.com/kb/HT214058)
- [seclists.org](http://seclists.org/fulldisclosure/2024/Jan/34)
- [seclists.org](http://seclists.org/fulldisclosure/2024/Jan/37)
- [seclists.org](http://seclists.org/fulldisclosure/2024/Jan/38)
- [security.netapp.com](https://security.netapp.com/advisory/ntap-20240201-0005/)
- [forum.vmssoftware.com](https://forum.vmssoftware.com/viewtopic.php?f=8&t=8868)
- [github.com](https://github.com/bcdannyboy/CVE-2023-38545)
- [github.com](https://github.com/dbrugman/CVE-2023-38545-POC)
- [github.com](https://github.com/UTsweetyfish/CVE-2023-38545)
- [cert-portal.siemens.com](https://cert-portal.siemens.com/productcert/html/ssa-943925.html)
- [cert-portal.siemens.com](https://cert-portal.siemens.com/productcert/html/ssa-832273.html)
- [cert-portal.siemens.com](https://cert-portal.siemens.com/productcert/html/ssa-093430.html)
- [cert-portal.siemens.com](https://cert-portal.siemens.com/productcert/html/ssa-082556.html)
- [cert-portal.siemens.com](https://cert-portal.siemens.com/productcert/html/ssa-507364.html)

---
Source page: https://erroneo.us/security/cve/CVE-2023-38545/ · Security Digest: https://erroneo.us/security/ · More: https://erroneo.us/llms.txt