CVE-2026-55107 Kobako Vulnerable to Sandbox Escape: guest eval reaches host RCE via method_missing → public_send (any bound Service)

Kobako is a Ruby gem that embeds a Wasm-isolated mruby interpreter inside applications, allowing execution of untrusted Ruby scripts LLM-generated code, user formulas, student submissions, third-party plugins in-process without giving them access to host memory, files, network, or credentials. Fr...

CVE-2026-55107

The Kobako Ruby gem (versions 0.1.0 through 0.9.0 ) contains a critical sandbox escape vulnerability. The root cause is an unguarded Object#public_send sink in the transport dispatcher, which allows guest mruby scripts to execute arbitrary Ruby in the host process. Attackers can pivot through the...

CVE-2026-55107 Kobako Vulnerable to Sandbox Escape: guest eval reaches host RCE via method_missing → public_send (any bound Service)

Kobako is a Ruby gem that embeds a Wasm-isolated mruby interpreter inside applications, allowing execution of untrusted Ruby scripts LLM-generated code, user formulas, student submissions, third-party plugins in-process without giving them access to host memory, files, network, or credentials. Fr...

GHSA-7PWQ-Q9JF-539H kobako Sandbox Escape: guest eval reaches host RCE via method_missing → public_send (any bound Service)

Summary A guest mruby script running inside the Kobako sandbox can execute arbitrary Ruby in the host process, fully escaping the sandbox. Details A host embeds bound "Service" objects that guest scripts call across the wasm boundary through the transport dispatcher. The dispatcher passed the...

kobako Sandbox Escape: guest eval reaches host RCE via method_missing → public_send (any bound Service)

Summary A guest mruby script running inside the Kobako sandbox can execute arbitrary Ruby in the host process, fully escaping the sandbox. Details A host embeds bound "Service" objects that guest scripts call across the wasm boundary through the transport dispatcher. The dispatcher passed the...

kobako Sandbox Escape - guest eval reaches host RCE via method_missing → public_send (any bound Service)

Summary A guest mruby script running inside the Kobako sandbox can execute arbitrary Ruby in the host process, fully escaping the sandbox. Impact Complete sandbox escape leading to remote code execution in the host process, defeating the gem's central guarantee of isolating untrusted mruby script...

GitLab: Use of Ruby Forwardable module and runtime meta-programming may introduce vulnerabilities

I was digging through the gitlab-foss repository and noticed an interested pattern that seems to be adopted in a few places: the use of Forwardable with meta-programming over delegators, explicit attrreader methods or methodmissing. Heads up: the arbitrary file read vulnerability I demonstrate in...

shopify-scripts: Crash in mrb_ary_push

PoC === The following demonstrates a crash: def methodmissing end .00 %= begin0=0 00end Debug info ========== The crash happens in mrbarypush: 495│ mrbarypushmrbstate mrb, mrbvalue ary, mrbvalue elem 496│ 497│ struct RArray a = mrbaryptrary; 498├─ mrbint len = ARYLENa; gdb p a $1 = struct RArray...

shopify-scripts: SIGABRT - mirb and mruby

PoC ------------------- The following code triggers the bug attached as test.rb: def methodmissingm,e self.ff||=00end e Debug - mirb ------------------- x@x:/Desktop/test/mruby/bin$ gdb -q ./mirb Reading symbols from ./mirb...done. gdb r test.rb Starting program: /home/x/Desktop/test/mruby/bin/mi...

shopify-scripts: SIGABRT - method_missing - mark_context_stack

PoC ------------------- The following code triggers the bug attached as testmethodmissing.rb: def methodmissinge,0.n||=0 00end b Debug - mirb ------------------- gdb r testmethodmissing.rb Starting program: /home/x/Desktop/research/test/mruby/bin/mirb testmethodmissing.rb mirb - Embeddable...

shopify-scripts: Undefined method_missing null pointer dereference

It's possible to segfault mruby by undefining BasicObjectmethodmissing in certain cases. There is a fallback methodmissing C function mrbmethodmissing which is called in some cases when the VM fails to look up the methodmissing method: BasicObject.removemethod:methodmissing; 1.foo NoMethodError:...