CVE-2026-66338
MEDIUMDescription
A flaw was found in libsoup. The chunked transfer encoding parser uses a permissive parsing function for chunk sizes that silently accepts inputs violating RFC 9112, including leading whitespace, plus sign prefixes, and trailing invalid characters. When libsoup operates behind a strict frontend proxy, this parsing differential can be exploited to smuggle HTTP requests.
How to fix
No published remediation has been found for this vulnerability's affected products yet.
Mitigation guidance may be in the linked vendor advisories in the References section below.
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CVSS v3 Vector
Exploitability
Impact
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:C/C:L/I:L/A:N/E:U
Exploit Intelligence
Low risk: more likely to be exploited than 9% of all known CVEs.
References
Related Vulnerabilities
Other CWE-444 vulnerabilities, ordered by exploit likelihood. View all
| CVE | Severity | CVSS | EPSS | Exploited | Fix |
|---|---|---|---|---|---|
| CVE-2022-22536 | Critical | 10.0 | 98% | KEV | - |
| CVE-2025-61884 | High | 7.5 | 98% | KEV + Ransom | - |
| CVE-2020-9490 | High | 7.5 | 89% | - | Fix |
| CVE-2023-41265 | Critical | 9.6 | 88% | KEV + Ransom | - |
| CVE-2023-25690 | Critical | 9.8 | 85% | - | Fix |
| CVE-2022-32214 | Medium | 6.5 | 81% | - | Fix |
Common questions
How do I fix CVE-2026-66338?
No published fix for CVE-2026-66338 has been found yet. Check the linked vendor advisories for guidance as it becomes available.
Is CVE-2026-66338 being actively exploited?
Not that we know of. CVE-2026-66338 is not in the CISA Known Exploited Vulnerabilities catalog. Its EPSS score of 0.19% is the estimated probability that it will be exploited in the next 30 days. That is higher than 9% of all scored CVEs.
How severe is CVE-2026-66338?
CVE-2026-66338 has a CVSS v3 base score of 5.4, rated moderate. CVSS rates the technical impact if the vulnerability is exploited, not how likely that is, so weigh it alongside the exploit-prediction score when you decide what to patch first.
Embed a live status badge for CVE-2026-66338
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This product uses NVD data but is not endorsed or certified by the NVD. EPSS scores courtesy of FIRST.org (https://www.first.org/epss). Source: CISA KEV Catalog. Data as of 2026-08-24.