Opened 2 years ago

Closed 2 years ago

#2340 closed defect (duplicate)

decoded percent-encoded values written to logfiles

Reported by: mozai@… Owned by:
Priority: minor Milestone:
Component: nginx-core Version: 1.14.x
Keywords: logging Cc:
uname -a: Linux 5.14.17-x86_64-linode150 #1 SMP Thu Nov 11 13:17:05 EST 2021 x86_64 x86_64 x86_64 GNU/Linux
nginx -V: nginx version: nginx/1.14.0 (Ubuntu)
built with OpenSSL 1.1.1 11 Sep 2018
TLS SNI support enabled
configure arguments: --with-cc-opt='-g -O2 -fdebug-prefix-map=/build/nginx-H4cN7P/nginx-1.14.0=. -fstack-protector-strong -Wformat -Werror=format-security -fPIC -Wdate-time -D_FORTIFY_SOURCE=2' --with-ld-opt='-Wl,-Bsymbolic-functions -Wl,-z,relro -Wl,-z,now -fPIC' --prefix=/usr/share/nginx --conf-path=/etc/nginx/nginx.conf --http-log-path=/var/log/nginx/access.log --error-log-path=/var/log/nginx/error.log --lock-path=/var/lock/nginx.lock --pid-path=/run/ --modules-path=/usr/lib/nginx/modules --http-client-body-temp-path=/var/lib/nginx/body --http-fastcgi-temp-path=/var/lib/nginx/fastcgi --http-proxy-temp-path=/var/lib/nginx/proxy --http-scgi-temp-path=/var/lib/nginx/scgi --http-uwsgi-temp-path=/var/lib/nginx/uwsgi --with-debug --with-pcre-jit --with-http_ssl_module --with-http_stub_status_module --with-http_realip_module --with-http_auth_request_module --with-http_v2_module --with-http_dav_module --with-http_slice_module --with-threads --with-http_addition_module --with-http_geoip_module=dynamic --with-http_gunzip_module --with-http_gzip_static_module --with-http_image_filter_module=dynamic --with-http_sub_module --with-http_xslt_module=dynamic --with-stream=dynamic --with-stream_ssl_module --with-mail=dynamic --with-mail_ssl_module


Saw that bad requests that percent-encode nonprintable characters are breaking the nginx log files. currently it breaks logfile parsers, but I worry it could be used to inject out-of-band instructions into logfiles.

In /var/log/nginx/error.log:
2022/03/27 17:04:52 [error] 23762#23762: *1142443 "/srv/http/com.dandytype/
/" is not found (2: No such file or directory), client:, server:, request: "GET /%0A/ HTTP/1.1", host: ""

What I expected:
Logfile has one record per newline-terminated string

What I saw instead:
Logfile has two records for one event, neither matching the pattern for logfile records.

Other information:
I worry that writing decoded percent-encoded bytes could be used to insert nulls (%00) that could be used for buffer underruns in C, or insert Unicode codepoints to obfuscate requests by bad actors.

Change History (1)

comment:1 by Maxim Dounin, 2 years ago

Resolution: duplicate
Status: newclosed

Duplicate of #191.

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