Skip to content

feat(934200): detect Server-Side Template Injection (SSTI) attacks #4600

New issue

Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.

Sign up for GitHub

By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement. We’ll occasionally send you account related emails.

Already on GitHub? Sign in to your account

Merged
fzipi merged 4 commits into from
Apr 25, 2026
+221 −0
Merged

feat(934200): detect Server-Side Template Injection (SSTI) attacks #4600

Show file tree
Hide file tree
Changes from all commits
Commits
Show all changes
4 commits
Select commit Hold shift + click to select a range
1bcc28a
feat(934175): detect Server-Side Template Injection (SSTI) attacks
Mar 30, 2026
bc41030
fix(934175): add regex-assembly file and regenerate conf
Apr 17, 2026
4546e03
test(934175): add regression tests for SSTI detection rule
Apr 17, 2026
c32323e
fix: renumber SSTI rule from 934175 to 934200
Apr 20, 2026
File filter

Filter by extension

Filter by extension
Conversations
Failed to load comments.
Loading
Jump to
Jump to file
Failed to load files.
Loading
Diff view
Diff view
38 changes: 38 additions & 0 deletions regex-assembly/934200.ra
View file
Open in desktop
Original file line number Diff line number Diff line change
@@ -0,0 +1,38 @@
##! Please refer to the documentation at
##! https://coreruleset.org/docs/development/regex_assembly/.

##! Detect Server-Side Template Injection (SSTI) attacks at PL1.
##! Matches template delimiters only when they contain code execution
##! indicators: arithmetic (*), dunder access (__), or function calls (().
##! This is stricter than 934180 (PL2) which matches broad template syntax.

##! Execution indicators: patterns that suggest code execution
##! rather than simple variable interpolation.
##!> define exec-indicators (?:\*|__|\()

##! Jinja2/Twig: {{7*7}}, {{''.__class__}}, {{config.items()}}
##!> assemble
\{\{[^}]*?
##!=>
{{exec-indicators}}
##!=>
[^}]*?\}\}
##!<

##! Expression Language: #{runtime.exec('id')}, #{7*7}
##!> assemble
#\{[^}]*?
##!=>
{{exec-indicators}}
##!=>
[^}]*?\}
##!<

##! ERB/JSP: <%=7*7%>, <% system('id') %>
##!> assemble
<%=?\s*[^%]*?
##!=>
{{exec-indicators}}
##!=>
[^%]*?%>
##!<
32 changes: 32 additions & 0 deletions rules/REQUEST-934-APPLICATION-ATTACK-GENERIC.conf
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -273,6 +273,38 @@ SecRule REQUEST_FILENAME|REQUEST_COOKIES|REQUEST_COOKIES_NAMES|ARGS_NAMES|ARGS|X
setvar:'tx.rce_score=+%{tx.critical_anomaly_score}',\
setvar:'tx.inbound_anomaly_score_pl1=+%{tx.critical_anomaly_score}'"

#
# Detects SSTI (Server-Side Template Injection) attacks at PL1.
# Requires code execution indicators (arithmetic, dunder access, function calls)
# inside template syntax to reduce false positives.
# Examples: {{7*7}}, #{system('id')}, <%= 7*7 %>
#
# Regular expression generated from regex-assembly/934200.ra.
# To update the regular expression run the following shell script
# (consult https://coreruleset.org/docs/development/regex_assembly/ for details):
# crs-toolchain regex update 934200
#
SecRule REQUEST_COOKIES|REQUEST_COOKIES_NAMES|ARGS_NAMES|ARGS|XML:/* "@rx (?:\{\{[^\}]*?(?:[\(\*]|__)[^\}]*?\}|#\{[^\}]*?(?:[\(\*]|__)[^\}]*?)\}|<%=?[\s\x0b]*[^%]*?(?:[\(\*]|__)[^%]*?%>" \
"id:934200,\
phase:2,\
block,\
capture,\
t:none,t:urlDecodeUni,\
msg:'Server-Side Template Injection (SSTI) Attack',\
logdata:'Matched Data: %{TX.0} found within %{MATCHED_VAR_NAME}: %{MATCHED_VAR}',\
tag:'application-multi',\
tag:'platform-multi',\
tag:'attack-ssti',\
tag:'attack-injection-generic',\
tag:'paranoia-level/1',\
tag:'OWASP_CRS',\
tag:'OWASP_CRS/ATTACK-GENERIC',\
tag:'capec/1000/152/242',\
ver:'OWASP_CRS/4.26.0-dev',\
severity:'CRITICAL',\
setvar:'tx.rce_score=+%{tx.critical_anomaly_score}',\
setvar:'tx.inbound_anomaly_score_pl1=+%{tx.critical_anomaly_score}'"

SecRule TX:DETECTION_PARANOIA_LEVEL "@lt 2" "id:934013,phase:1,pass,nolog,tag:'OWASP_CRS',ver:'OWASP_CRS/4.26.0-dev',skipAfter:END-REQUEST-934-APPLICATION-ATTACK-GENERIC"
SecRule TX:DETECTION_PARANOIA_LEVEL "@lt 2" "id:934014,phase:2,pass,nolog,tag:'OWASP_CRS',ver:'OWASP_CRS/4.26.0-dev',skipAfter:END-REQUEST-934-APPLICATION-ATTACK-GENERIC"
#
Expand Down
151 changes: 151 additions & 0 deletions tests/regression/tests/REQUEST-934-APPLICATION-ATTACK-GENERIC/934200.yaml
View file
Open in desktop
Original file line number Diff line number Diff line change
@@ -0,0 +1,151 @@
---
meta:
author: "zoutjebot"
rule_id: 934200
tests:
# === Positive tests (should trigger) ===
- test_id: 1
desc: "Jinja2/Twig SSTI - arithmetic in double curly braces"
stages:
- input:
dest_addr: 127.0.0.1
headers:
Accept: "*/*"
Host: localhost
User-Agent: "OWASP CRS test agent"
method: GET
port: 80
uri: "/get?x=%7b%7b7*7%7d%7d"
version: HTTP/1.1
output:
log:
expect_ids: [934200]
- test_id: 2
desc: "Jinja2/Twig SSTI - dunder access in double curly braces"
stages:
- input:
dest_addr: 127.0.0.1
headers:
Accept: "*/*"
Host: localhost
User-Agent: "OWASP CRS test agent"
method: GET
port: 80
uri: "/get?x=%7b%7b%27%27.__class__.__mro__%7d%7d"
version: HTTP/1.1
output:
log:
expect_ids: [934200]
- test_id: 3
desc: "Expression Language SSTI - function call in hash curly"
stages:
- input:
dest_addr: 127.0.0.1
headers:
Accept: "*/*"
Host: localhost
User-Agent: "OWASP CRS test agent"
method: GET
port: 80
uri: "/get?x=%23%7bruntime.exec(%27id%27)%7d"
version: HTTP/1.1
output:
log:
expect_ids: [934200]
- test_id: 4
desc: "ERB SSTI - arithmetic in angle bracket percent"
stages:
- input:
dest_addr: 127.0.0.1
headers:
Accept: "*/*"
Host: localhost
User-Agent: "OWASP CRS test agent"
method: GET
port: 80
uri: "/get?x=%3c%25%3d7*7%25%3e"
version: HTTP/1.1
output:
log:
expect_ids: [934200]
- test_id: 5
desc: "ERB SSTI - function call with system command"
stages:
- input:
dest_addr: 127.0.0.1
headers:
Accept: "*/*"
Host: localhost
User-Agent: "OWASP CRS test agent"
method: GET
port: 80
uri: "/get?x=%3c%25%20system(%27id%27)%20%25%3e"
version: HTTP/1.1
output:
log:
expect_ids: [934200]
- test_id: 6
desc: "Expression Language SSTI - arithmetic in hash curly"
stages:
- input:
dest_addr: 127.0.0.1
headers:
Accept: "*/*"
Host: localhost
User-Agent: "OWASP CRS test agent"
method: GET
port: 80
uri: "/get?x=%23%7b7*7%7d"
version: HTTP/1.1
output:
log:
expect_ids: [934200]
# === Negative tests (should NOT trigger) ===
- test_id: 7
desc: "Legitimate template variable - no execution indicators"
stages:
- input:
dest_addr: 127.0.0.1
headers:
Accept: "*/*"
Host: localhost
User-Agent: "OWASP CRS test agent"
method: GET
port: 80
uri: "/get?x=%7b%7busername%7d%7d"
version: HTTP/1.1
output:
log:
no_expect_ids: [934200]
- test_id: 8
desc: "Legitimate ERB output tag - simple variable"
stages:
- input:
dest_addr: 127.0.0.1
headers:
Accept: "*/*"
Host: localhost
User-Agent: "OWASP CRS test agent"
method: GET
port: 80
uri: "/get?x=%3c%25%3dtitle%25%3e"
version: HTTP/1.1
output:
log:
no_expect_ids: [934200]
- test_id: 9
desc: "Legitimate EL variable - no execution indicators"
stages:
- input:
dest_addr: 127.0.0.1
headers:
Accept: "*/*"
Host: localhost
User-Agent: "OWASP CRS test agent"
method: GET
port: 80
uri: "/get?x=%23%7bname%7d"
version: HTTP/1.1
output:
log:
no_expect_ids: [934200]
Loading