cbcvebase.
CVE-2016-0736
published 2017-07-27

CVE-2016-0736: In Apache HTTP Server versions 2.4.0 to 2.4.23, mod_session_crypto was encrypting its data/cookie using the configured ciphers with possibly either CBC or ECB…

PriorityP183high7.5CVSS 3.0
AVNACLPRNUINSUCHINAN
ITWEXPLOITVulnCheck KEVRansomware
Exploited in the wild
EPSS
49.02%
98.8th percentile
In Apache HTTP Server versions 2.4.0 to 2.4.23, mod_session_crypto was encrypting its data/cookie using the configured ciphers with possibly either CBC or ECB modes of operation (AES256-CBC by default), hence no selectable or builtin authenticated encryption. This made it vulnerable to padding oracle attacks, particularly with CBC.

Affected

22 ranges
VendorProductVersion rangeFixed in
apachehttp_server
apachehttp_server
apachehttp_server
apachehttp_server
apachehttp_server
apachehttp_server
apachehttp_server
apachehttp_server
apachehttp_server
apachehttp_server
apachehttp_server
apachehttp_server
apachehttp_server
apachehttp_server
apachehttp_server
apachehttp_server
apachehttp_server
apache_software_foundationapache_http_server
applemacos_high_sierra
applemacos_high_sierra_10.13.1_security_update_2017-001_sierra_and_security_update_20
applemacos_sierra_10.12.4_security_update_2017-001_el_capitan_and_security_update_201
debianapache2< apache2 2.4.25-1 (bookworm)apache2 2.4.25-1 (bookworm)

Detection & IOCsextracted from sources · hover to see the quote

cookiesession
pathmodules/session/mod_session_crypto.c
  • Detect padding oracle probing by monitoring for high volumes of requests to the same endpoint with slightly modified 'session' cookie values (single base64 character changes at the end of the cookie), correlating with alternating 'username' present / absent response bodies.
  • Alert on the 'X-Replace-Session' response header being present, as this is the mechanism used by the attacker-controlled application to inject arbitrary session content after a successful padding oracle encrypt operation.
  • Flag use of the python-paddingoracle library (PaddingOracle / BadPaddingException imports) in network tooling or scripts found on hosts, as it is the specific library used to automate exploitation of this CVE.
  • Identify Apache HTTP Server versions 2.4.0–2.4.23 running mod_session_crypto; these are confirmed vulnerable. Upgrade to 2.4.25 or later.
  • ·The vulnerability is only exploitable when mod_session, mod_session_crypto, and mod_session_cookie are all enabled together. The SessionCryptoPassphrase directive must be set. Deployments not using this combination are not affected.
  • ·The default cipher mode is AES256-CBC; CBC mode is specifically what enables the padding oracle attack. ECB mode is also vulnerable but for different reasons. Authenticated encryption (e.g., GCM) was not available prior to the fix.

CVSS provenance

nvdv3.07.5HIGHCVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N
nvdv2.05.0MEDIUMAV:N/AC:L/Au:N/C:P/I:N/A:N
osv7.5HIGH
vulncheck7.5HIGH
vendor_debian7.5HIGH
vendor_redhat7.5HIGH
vendor_ubuntu7.5HIGH
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