CVE-2016-4975 | mod_userdir CRLF injection

Possible CRLF injection allowing HTTP response splitting attacks for sites which use mod_userdir. This issue was mitigated by changes made in 2.4.25 and 2.2.32 which prohibit CR or LF injection into the "Location" or other outbound header key or value. Fixed in Apache HTTP Server 2.4.25 (Affected 2.4.1-2.4.23). Fixed in Apache HTTP Server 2.2.32 (Affected 2.2.0-2.2.31).

Published: 2018-08-14 Last update: 2024-11-21 Assigner: [email protected] Source: [email protected]
NVD Status：Modified，CVE State: published
View at NVD, CVE.org, EUVD

CVE-2016-4975 is rated Moderate Risk (56.9/100): CVSS Medium severity, with high exploitation likelihood (EPSS 73.27%, 99th percentile). EPSS ranks this CVE among the most likely to be exploited in the near term. High exploitation likelihood—assess exposure and prioritize remediation.

Risk is dynamic; we continuously reassess and refresh what is shown on this page as upstream context changes.

Exploit prediction scoring system (EPSS) score for CVE-2016-4975

EPSS lead: Daily EPSS estimates relative likelihood of exploitation; percentile ranks this CVE among scored vulnerabilities (higher = more severe relative rank).

# Date Old EPSS score New EPSS score Delta (New - Old)
1 2026-04-05 75.34% 73.27% -2.07%
2 2026-03-13 73.01% 75.34% +2.33%
3 2026-03-04 — 73.01% —

Full EPSS history (46 records total)

Common vulnerability scoring system (CVSS) metrics for CVE-2016-4975

CVSS metrics for this CVE.

Base score Version Severity Vector Exploitability Impact Score source
6.1 3.0 MEDIUM
CVSS:3.0/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N Click to expand
Attack vector (AV:N)
Could be attacked over the internet or any normal routed network—not just someone sitting at the machine.
Attack complexity (AC:L)
Once they can reach the bug, pulling it off is straightforward—no weird race conditions or rare setup.
Privileges required (PR:N)
No account or special rights needed—anonymous or random user is enough.
User interaction (UI:R)
A real person has to do something—click, install, enable—otherwise it doesn’t land.
Scope (S:C)
Breaking this can reach past the original component and bite other resources—bigger blast radius.
Confidentiality (C:L)
Some sensitive info could get out, but not a total data dump.
Integrity (I:L)
Attackers could change some data, but it’s limited—not everything goes.
Availability (A:N)
Service keeps running; no real outage angle.
 2.8 2.7 [email protected]
4.3 2.0 MEDIUM
AV:N/AC:M/Au:N/C:N/I:P/A:N Click to expand
Access vector (AV:N)
Can be exploited remotely over network reachability.
Access complexity (AC:M)
Exploitation needs some favorable conditions, but not exceptional ones.
Authentication (AU:N)
No authentication is required.
Confidentiality impact (C:N)
No confidentiality impact.
Integrity impact (I:P)
Partial integrity impact.
Availability impact (A:N)
No availability impact.
 8.6 2.9 [email protected]

Weakness enumeration for CVE-2016-4975

OS Trackers for CVE-2016-4975

vendor priority summary link
debian low CVE-2016-4975 low priority: Debian including 1 source packages (apache2), 5 status rows across 5 suites (bookworm, bullseye, forky, sid, trixie): resolved 5. https://security-tracker.debian.org/tracker/CVE-2016-4975
redhat medium — https://access.redhat.com/security/cve/CVE-2016-4975
suse low CVE-2016-4975 severity low: SUSE including 26 source package names (apache2, apache2-2.4.16-20.19.1, …), 123 product×package rows across 26 product lines (SUSE Enterprise Storage 4, SUSE Linux Enterprise High Performance Computing 12 SP5, … (26 product lines)): Fixed 99, Known Not Affected 24. https://www.suse.com/security/cve/CVE-2016-4975/
ubuntu low CVE-2016-4975 low priority: Ubuntu including 1 source packages (apache2), 6 status rows across 6 suites (bionic, cosmic, disco, trusty, upstream, xenial): not-affected 3, released 3. https://ubuntu.com/security/CVE-2016-4975

Affected software / configurations for CVE-2016-4975

Vendor Product Version Raw CPE
apache http_server 2.2.0 cpe:2.3:a:apache:http_server:2.2.0:*:*:*:*:*:*:*
apache http_server 2.2.2 cpe:2.3:a:apache:http_server:2.2.2:*:*:*:*:*:*:*
apache http_server 2.2.3 cpe:2.3:a:apache:http_server:2.2.3:*:*:*:*:*:*:*
apache http_server 2.2.4 cpe:2.3:a:apache:http_server:2.2.4:*:*:*:*:*:*:*
apache http_server 2.2.6 cpe:2.3:a:apache:http_server:2.2.6:*:*:*:*:*:*:*
apache http_server 2.2.8 cpe:2.3:a:apache:http_server:2.2.8:*:*:*:*:*:*:*
apache http_server 2.2.9 cpe:2.3:a:apache:http_server:2.2.9:*:*:*:*:*:*:*
apache http_server 2.2.10 cpe:2.3:a:apache:http_server:2.2.10:*:*:*:*:*:*:*
apache http_server 2.2.11 cpe:2.3:a:apache:http_server:2.2.11:*:*:*:*:*:*:*
apache http_server 2.2.12 cpe:2.3:a:apache:http_server:2.2.12:*:*:*:*:*:*:*
apache http_server 2.2.13 cpe:2.3:a:apache:http_server:2.2.13:*:*:*:*:*:*:*
apache http_server 2.2.14 cpe:2.3:a:apache:http_server:2.2.14:*:*:*:*:*:*:*
apache http_server 2.2.15 cpe:2.3:a:apache:http_server:2.2.15:*:*:*:*:*:*:*
apache http_server 2.2.16 cpe:2.3:a:apache:http_server:2.2.16:*:*:*:*:*:*:*
apache http_server 2.2.17 cpe:2.3:a:apache:http_server:2.2.17:*:*:*:*:*:*:*
apache http_server 2.2.18 cpe:2.3:a:apache:http_server:2.2.18:*:*:*:*:*:*:*
apache http_server 2.2.19 cpe:2.3:a:apache:http_server:2.2.19:*:*:*:*:*:*:*
apache http_server 2.2.20 cpe:2.3:a:apache:http_server:2.2.20:*:*:*:*:*:*:*
apache http_server 2.2.21 cpe:2.3:a:apache:http_server:2.2.21:*:*:*:*:*:*:*
apache http_server 2.2.22 cpe:2.3:a:apache:http_server:2.2.22:*:*:*:*:*:*:*
apache http_server 2.2.23 cpe:2.3:a:apache:http_server:2.2.23:*:*:*:*:*:*:*
apache http_server 2.2.24 cpe:2.3:a:apache:http_server:2.2.24:*:*:*:*:*:*:*
apache http_server 2.2.25 cpe:2.3:a:apache:http_server:2.2.25:*:*:*:*:*:*:*
apache http_server 2.2.26 cpe:2.3:a:apache:http_server:2.2.26:*:*:*:*:*:*:*
apache http_server 2.2.27 cpe:2.3:a:apache:http_server:2.2.27:*:*:*:*:*:*:*
apache http_server 2.2.29 cpe:2.3:a:apache:http_server:2.2.29:*:*:*:*:*:*:*
apache http_server 2.2.31 cpe:2.3:a:apache:http_server:2.2.31:*:*:*:*:*:*:*
apache http_server 2.4.1 cpe:2.3:a:apache:http_server:2.4.1:*:*:*:*:*:*:*
apache http_server 2.4.2 cpe:2.3:a:apache:http_server:2.4.2:*:*:*:*:*:*:*
apache http_server 2.4.3 cpe:2.3:a:apache:http_server:2.4.3:*:*:*:*:*:*:*
apache http_server 2.4.4 cpe:2.3:a:apache:http_server:2.4.4:*:*:*:*:*:*:*
apache http_server 2.4.6 cpe:2.3:a:apache:http_server:2.4.6:*:*:*:*:*:*:*
apache http_server 2.4.7 cpe:2.3:a:apache:http_server:2.4.7:*:*:*:*:*:*:*
apache http_server 2.4.9 cpe:2.3:a:apache:http_server:2.4.9:*:*:*:*:*:*:*
apache http_server 2.4.10 cpe:2.3:a:apache:http_server:2.4.10:*:*:*:*:*:*:*
apache http_server 2.4.12 cpe:2.3:a:apache:http_server:2.4.12:*:*:*:*:*:*:*
apache http_server 2.4.16 cpe:2.3:a:apache:http_server:2.4.16:*:*:*:*:*:*:*
apache http_server 2.4.17 cpe:2.3:a:apache:http_server:2.4.17:*:*:*:*:*:*:*
apache http_server 2.4.18 cpe:2.3:a:apache:http_server:2.4.18:*:*:*:*:*:*:*
apache http_server 2.4.20 cpe:2.3:a:apache:http_server:2.4.20:*:*:*:*:*:*:*
apache http_server 2.4.23 cpe:2.3:a:apache:http_server:2.4.23:*:*:*:*:*:*:*

References for CVE-2016-4975

URL Tags
http://www.securityfocus.com/bid/105093 Third Party Advisory VDB Entry
https://httpd.apache.org/security/vulnerabilities_22.html#CVE-2016-4975 Vendor Advisory
https://httpd.apache.org/security/vulnerabilities_24.html#CVE-2016-4975 Vendor Advisory
https://lists.apache.org/thread.html/56c2e7cc9deb1c12a843d0dc251ea7fd3e7e80293cde02fcd65286ba%40%3Ccvs.httpd.apache.org%3E
https://lists.apache.org/thread.html/84a3714f0878781f6ed84473d1a503d2cc382277e100450209231830%40%3Ccvs.httpd.apache.org%3E
https://lists.apache.org/thread.html/8d63cb8e9100f28a99429b4328e4e7cebce861d5772ac9863ba2ae6f%40%3Ccvs.httpd.apache.org%3E
https://lists.apache.org/thread.html/f7f95ac1cd9895db2714fa3ebaa0b94d0c6df360f742a40951384a53%40%3Ccvs.httpd.apache.org%3E
https://lists.apache.org/thread.html/r04e89e873d54116a0635ef2f7061c15acc5ed27ef7500997beb65d6f%40%3Ccvs.httpd.apache.org%3E
https://lists.apache.org/thread.html/r57608dc51b79102f3952ae06f54d5277b649c86d6533dcd6a7d201f7%40%3Ccvs.httpd.apache.org%3E
https://lists.apache.org/thread.html/r75cbe9ea3e2114e4271bbeca7aff96117b50c1b6eb7c4772b0337c1f%40%3Ccvs.httpd.apache.org%3E
https://lists.apache.org/thread.html/r9ea3538f229874c80a10af473856a81fbf5f694cd7f471cc679ba70b%40%3Ccvs.httpd.apache.org%3E
https://lists.apache.org/thread.html/r9f93cf6dde308d42a9c807784e8102600d0397f5f834890708bf6920%40%3Ccvs.httpd.apache.org%3E
https://lists.apache.org/thread.html/rb14daf9cc4e28d18cdc15d6a6ca74e565672fabf7ad89541071d008b%40%3Ccvs.httpd.apache.org%3E
https://lists.apache.org/thread.html/rc998b18880df98bafaade071346690c2bc1444adaa1a1ea464b93f0a%40%3Ccvs.httpd.apache.org%3E
https://lists.apache.org/thread.html/rcc44594d4d6579b90deccd4536b5d31f099ef563df39b094be286b9e%40%3Ccvs.httpd.apache.org%3E
https://lists.apache.org/thread.html/rd18c3c43602e66f9cdcf09f1de233804975b9572b0456cc582390b6f%40%3Ccvs.httpd.apache.org%3E
https://lists.apache.org/thread.html/rd336919f655b7ff309385e34a143e41c503e133da80414485b3abcc9%40%3Ccvs.httpd.apache.org%3E
https://lists.apache.org/thread.html/rdca61ae990660bacb682295f2a09d34612b7bb5f457577fe17f4d064%40%3Ccvs.httpd.apache.org%3E
https://lists.apache.org/thread.html/re1e3a24664d35bcd0a0e793e0b5fc6ca6c107f99a1b2c545c5d4b467%40%3Ccvs.httpd.apache.org%3E
https://lists.apache.org/thread.html/re3d27b6250aa8548b8845d314bb8a350b3df326cacbbfdfe4d455234%40%3Ccvs.httpd.apache.org%3E
https://lists.apache.org/thread.html/rf6449464fd8b7437704c55f88361b66f12d5b5f90bcce66af4be4ba9%40%3Ccvs.httpd.apache.org%3E
https://lists.apache.org/thread.html/rfbaf647d52c1cb843e726a0933f156366a806cead84fbd430951591b%40%3Ccvs.httpd.apache.org%3E
https://security.netapp.com/advisory/ntap-20180926-0006/ Third Party Advisory
https://support.hpe.com/hpsc/doc/public/display?docLocale=en_US&docId=emr_na-hpesbux03908en_us
cvelogic Threat Intelligence