HTTP Response Splitting

published 2020-07-27 6 y ago modified 2026-06-17 4 mo ago also GHSA-f97h-2pfx-f59f , PYSEC-2020-151 , EUVD-2020-0233

cvss: 5.3; version 3.1, CNA
cisa kev: Not listed; not in CISA's catalog
epss: 1.4%; EPSS 1.4% chance of exploitation in 30 days, percentile 72%
public exploits: 0; none known

Uvicorn before 0.11.7 is vulnerable to HTTP response splitting. CRLF sequences are not escaped in the value of HTTP headers. Attackers can exploit this to add arbitrary headers to HTTP responses, or even return an arbitrary response body, whenever crafted input is used to construct HTTP headers.

Patch / fix

fixed in 2 distros 1

pypi uvicorn 0.11.7
encode uvicorn 0.11.7

python-uvicorn Debian 14, Debian 13, Debian 12 0.13.3-1

debian advisories DEBIAN-CVE-2020-7695

Vendor advisories

What the vendors themselves say about their products: affected, fixed or not affected, and what to do.

red hat product security vex CVE-2020-7695 updated 2025-11-21 cvss 7.5

uvicorn: crafted input leads to HTTP response splitting

Red Hat All currently supported Red Hat products
not affected: vulnerable code not present

Red Hat CSAF VEX © Red Hat, Inc., from https://security.access.redhat.com/data/csaf/v2/vex/; changed: reduced to product statuses and remediations. CC BY 4.0 · csaf

Exploit prediction

1.39% chance of exploitation in the next 30 days, higher than 72% of all scored CVEs (FIRST EPSS, 2026-11-08).

Exploits and checks

snyk.io https://snyk.io/vuln/SNYK-PYTHON-UVICORN-570471 referenced PoC, tagged "exploit" by a source, unverified

CVSS scores

assigned by	version	score	vector
CNA	3.1	5.3	CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N/E:P/RL:U/RC:C
CNA	3.1	5.3	CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N
NVD	3.1	5.3	CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N
NVD	2.0	5.0	AV:N/AC:L/Au:N/C:N/I:P/A:N
GitHub	3.1	7.5	CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N

Affected packages

ecosystem	package	affected	fixed in
pypi	uvicorn	<0.11.7	0.11.7

Affected products

n/a uvicorn

Classification

Weakness

CWE-74 Improper Neutralization of Special Elements in Output Used by a Downstream Component

References

snyk.io /vuln/SNYK-PYTHON-UVICORN-570471
web, exploit, third-party-advisory, advisory
github.com /encode/uvicorn
package, third-party-advisory, web
nvd.nist.gov /vuln/detail/CVE-2020-7695
advisory
github.com /pypa/advisory-database/tree/main/vulns/uvicorn/PYSEC-2020-151.yaml
web
github.com /advisories/GHSA-f97h-2pfx-f59f
advisory

Sources

Fencer Vulns keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.

Summary