Re: log4j trivial RCE (similar to ShellShock) - "Log4Shell" CVE-2021-44228



From what I've been seeing, only version 2.x seems to be vulnerable, and 1.x is not, however nothing seems to be certain about that.

Have you seen any hard confirmation yet whether 1.x is vulnerable?


On Fri, 10 Dec 2021, Royce Williams wrote:

This one is developing quickly, so I'll push updates here as I discover them:
Royce Williams
Tech Solvency
On Fri, Dec 10, 2021 at 7:21 AM Royce Williams <royce@...> wrote:
Summary (Dan Goodin):
Log4j takes a log message, interprets it as a URL and goes out and fetches it. It will even execute JavaScript in URLs
with full privileges of the main program. Exploits are triggered inside  log messages using the ${} syntax. Easy peasy.
Who is affected:
- Servers and clients that run Java and also log anything using the log4j framework
- log4j 2.x confirmed, and probably log4j 1.x also
- Don't forget appliances that use Java server components
- Downstream projects that include log4j, including Apache Struts, Solr, etc.
Required to fully mitigate:
- Upgrade Log4j 2.15.0
- requires Java 8
Exploitation: active:
Mitigations - easiest:
- (@MalwareTechBlog): If you can't upgrade log4j, you can mitigate the RCE vulnerability by setting
log4j2.formatMsgNoLookups to True (-Dlog4j2.formatMsgNoLookups=true in JVM command line).
Mitigations - official project itself (
Users of Log4j 2.10 or greater may add -Dlog4j.formatMsgNoLookups=true as a command line option or add
log4j.formatMsgNoLookups=true to a file on the classpath to prevent lookups in log event
Users since Log4j 2.7 may specify %m{nolookups} in the PatternLayout configuration to prevent lookups in log event
Remove the JndiLookup and JndiManager classes from the log4j-core jar. Removal of the JndiManager will cause the
JndiContextSelector and JMSAppender to no longer function.
Mitigations - harder:
- WAF to limit exploit queries
- egress filtering to block unexpected outbound traffic
Exploit detection:
Good threads and summaries:
- (German)
Royce Williams
Tech Solvency

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