CVE-2026-6253 proxy credentials leak over redirect-to proxy
An attacker can steal proxy credentials when curl follows redirects between different proxy configurations, exposing sensitive authentication data.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-6253?
CVE-2026-6253 is a medium-severity vulnerability in Haxx Curl, published on 13 May 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Official description
curl might erroneously pass on credentials for a first proxy to a second proxy.
This can happen when the following conditions are true:
1. curl is setup to use specific different proxies for different URL schemes 2. the first proxy needs credentials 3. the second proxy uses no credentials 4. while using the first proxy (using say `http://`), curl is asked to follow a redirect to a URL using another scheme (say `https://`), accessed using a second, different, proxy
Weakness: CWE-522
Which versions are affected by CVE-2026-6253?
It affects 1 product.
Products include Haxx Curl.
How do I fix CVE-2026-6253?
Upgrade to a fixed version.
Is CVE-2026-6253 being exploited?
It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-6253 exists.
Other vulnerabilities in Haxx Curl
Sources
Also known as ALPINE-CVE-2026-6253, AZL-86666, AZL-86676, BELL-CVE-2026-6253, CURL-CVE-2026-6253, DEBIAN-CVE-2026-6253 and 8 more.