CVE-2026-66338: 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 lead

mediumCVSS 5.4CVE-2026-66338

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.

Details

Source: NVD Recent CVEs (US · database · site)
Severity: medium — CVSS 5.4
Published: 2026-07-24
Last updated: 2026-07-27
Exploitation: Not in CISA KEV at last sync

Original advisory: https://nvd.nist.gov/vuln/detail/CVE-2026-66338

Exploitation outlook

EPSS (FIRST.org) estimates each CVE’s probability of exploitation in the next 30 days — here is the CSIRTS.com read on those numbers.

Low exploitation riskCVE-2026-663380.17% 30-day exploitation probability — currently an unlikely target, but scores change as exploit code circulates. Riskier than 7% of all scored CVEs.

Referenced CVEs

CVE	CSIRTS overview	External
CVE-2026-66338	coverage & exploitation status	NVD · CVE.org

Recent advisories for libsoup. The chunked

A cluster of recent advisories against the same product widens the attack surface — attackers routinely chain freshly published CVEs on one product, so review these together.

highCVE-2026-15709: A flaw was found in libsoup's WebSocket implementation when using the permessage-deflate exten…nvd · 2026-07-14

CVE-2026-66338: 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 lead

Details

Exploitation outlook

Referenced CVEs

Recent advisories for libsoup. The chunked

More from NVD Recent CVEs