CVE-2024-9681: HSTS subdomain overwrites parent cache entry

Vulnerability summary

CVE-2024-9681 is a medium (CVSS 6.5) Incorrect Comparison vulnerability in curl. EPSS estimates a 1.99% chance of exploitation in the next 30 days, higher than 80.6% of scored vulnerabilities. 1 public exploit is recorded.

Timeline

1. 06-11-2024
   PublishedVulnerability first disclosed.
2. 03-11-2025
   Last modifiedVulnerability information updated.

Description

When curl is asked to use HSTS, the expiry time for a subdomain might overwrite a parent domain's cache entry, making it end sooner or later than otherwise intended. This affects curl using applications that enable HSTS and use URLs with the insecure `HTTP://` scheme and perform transfers with hosts like `x.example.com` as well as `example.com` where the first host is a subdomain of the second host. (The HSTS cache either needs to have been populated manually or there needs to have been previous HTTPS accesses done as the cache needs to have entries for the domains involved to trigger this problem.) When `x.example.com` responds with `Strict-Transport-Security:` headers, this bug can make the subdomain's expiry timeout *bleed over* and get set for the parent domain `example.com` in curl's HSTS cache. The result of a triggered bug is that HTTP accesses to `example.com` get converted to HTTPS for a different period of time than what was asked for by the origin server. If `example.com` for example stops supporting HTTPS at its expiry time, curl might then fail to access `http://example.com` until the (wrongly set) timeout expires. This bug can also expire the parent's entry *earlier*, thus making curl inadvertently switch back to insecure HTTP earlier than otherwise intended.

• CWE-697Incorrect ComparisonThe product compares two entities in a security-relevant context, but the comparison is incorrect.