Gnark out-of-memory during deserialization with crafted inputs
Thanks @pventuzelo for reporting.
From the correspondence:
Hi,
We (Fuzzinglabs & Lambdaclass) found that during deserialization of certain files representing a VerifyingKey, an excessive memory allocation is happening consuming a lot of resources and even triggering a crash with the error fatal error: runtime: out of memory.
Please find the details below:
Vulnerability Details
- Severity: Critical -> DoS
- Affected Component: Deserialization
Environment
-
Compiler Version: go version go1.22.2 linux/amd64
-
Distro Version: Ubuntu 24.04.1 LTS
-
Additional Environment Details:
[github.com/consensys/gnark](http://github.com/consensys/gnark) v0.11.0[github.com/consensys/gnark-crypto](http://github.com/consensys/gnark-crypto) v0.14.1-0.20240909142611-e6b99e74cec1
Steps to Reproduce
You can download the needed files here: https://drive.google.com/drive/folders/1KQ5I3vv4bUllvqbatGappwbAkIcR2NI_?usp=sharing
You have to run
go run gnark_poc.go
in a terminal.
Running the provided code will result in a memory crash or an extremely large memory allocation, which can be observed using the following command:
go tool pprof -web mem.pprof
Root Cause Analysis
The provided code loads a VerifyingKey from old.vk by calling the ReadFrom function. This function is implemented in backend/groth16/bn254/marshal.go within the gnark library.
The provided example uses the elliptic curve BN-254, so the code resides in the backend/groth16/bn254/ repertory. However, the same error exists in other repertories, such as backend/groth16/bls12-377/.
At line 207, a slice is allocated with a length of nbCommitments. This variable is directly extracted from the deserialized file, which, in our case, has a value of 2,327,186,600. This large value may be too big for some configurations, leading to memory allocations of approximately ±1 TB, as observed with pprof.
Detailed Behavior
go run gnark_poc.go
fatal error: runtime: out of memory
runtime stack:
runtime.throw({0x5fe946?, 0x2052ae?})
/usr/lib/go-1.22/src/runtime/panic.go:1023 +0x5c fp=0x7ffd65b321a0 sp=0x7ffd65b32170 pc=0x438a9c
runtime.sysMapOS(0xc000400000, 0x8ab6400000)
/usr/lib/go-1.22/src/runtime/mem_linux.go:167 +0x11b fp=0x7ffd65b321e0 sp=0x7ffd65b321a0 pc=0x418bbb
runtime.sysMap(0xc000400000, 0x8ab6400000, 0x7b19c8?)
/usr/lib/go-1.22/src/runtime/mem.go:155 +0x34 fp=0x7ffd65b32200 sp=0x7ffd65b321e0 pc=0x418634
runtime.(*mheap).grow(0x7a17c0, 0x455b066?)
/usr/lib/go-1.22/src/runtime/mheap.go:1534 +0x236 fp=0x7ffd65b32270 sp=0x7ffd65b32200 pc=0x42b176
runtime.(*mheap).allocSpan(0x7a17c0, 0x455b066, 0x0, 0x1)
/usr/lib/go-1.22/src/runtime/mheap.go:1246 +0x1b0 fp=0x7ffd65b32310 sp=0x7ffd65b32270 pc=0x42a850
runtime.(*mheap).alloc.func1()
/usr/lib/go-1.22/src/runtime/mheap.go:964 +0x5c fp=0x7ffd65b32358 sp=0x7ffd65b32310 pc=0x42a2fc
runtime.systemstack(0x46d79f)
/usr/lib/go-1.22/src/runtime/asm_amd64.s:509 +0x4a fp=0x7ffd65b32368 sp=0x7ffd65b32358 pc=0x46912a
goroutine 1 gp=0xc0000061c0 m=0 mp=0x798ca0 [running]:
runtime.systemstack_switch()
/usr/lib/go-1.22/src/runtime/asm_amd64.s:474 +0x8 fp=0xc000031b68 sp=0xc000031b58 pc=0x4690c8
runtime.(*mheap).alloc(0x5bc040?, 0xc00012bb08?, 0xa0?)
/usr/lib/go-1.22/src/runtime/mheap.go:958 +0x5b fp=0xc000031bb0 sp=0xc000031b68 pc=0x42a25b
runtime.(*mcache).allocLarge(0xc000126510?, 0x8ab60ca800, 0x1)
/usr/lib/go-1.22/src/runtime/mcache.go:234 +0x87 fp=0xc000031c00 sp=0xc000031bb0 pc=0x4176e7
runtime.mallocgc(0x8ab60ca800, 0x5d92a0, 0x1)
/usr/lib/go-1.22/src/runtime/malloc.go:1165 +0x597 fp=0xc000031c88 sp=0xc000031c00 pc=0x40ef97
runtime.makeslice(0xc00011c180?, 0x0?, 0x2?)
/usr/lib/go-1.22/src/runtime/slice.go:107 +0x49 fp=0xc000031cb0 sp=0xc000031c88 pc=0x4500c9
[github.com/consensys/gnark/backend/groth16/bn254.(*VerifyingKey).readFrom(0xc0001b7088](http://github.com/consensys/gnark/backend/groth16/bn254.(*VerifyingKey).readFrom(0xc0001b7088), {0x6598a0, 0xc00011dc50}, 0x0)
/home/raunan/go/pkg/mod/[github.com/!ronan!thoraval/gnark@v0.0.0-20241007163125-4c0a7511c3d1/backend/groth16/bn254/marshal.go:214](http://github.com/!ronan!thoraval/gnark@v0.0.0-20241007163125-4c0a7511c3d1/backend/groth16/bn254/marshal.go:214) +0x765 fp=0xc000031ea8 sp=0xc000031cb0 pc=0x59b205
[github.com/consensys/gnark/backend/groth16/bn254.(*VerifyingKey).ReadFrom(0x100469020](http://github.com/consensys/gnark/backend/groth16/bn254.(*VerifyingKey).ReadFrom(0x100469020)?, {0x6598a0?, 0xc00011dc50?})
/home/raunan/go/pkg/mod/[github.com/!ronan!thoraval/gnark@v0.0.0-20241007163125-4c0a7511c3d1/backend/groth16/bn254/marshal.go:166](http://github.com/!ronan!thoraval/gnark@v0.0.0-20241007163125-4c0a7511c3d1/backend/groth16/bn254/marshal.go:166) +0x1f fp=0xc000031ed8 sp=0xc000031ea8 pc=0x59aa5f
main.main()
/home/raunan/gnark_poc/gnark_poc/gnark_poc.go:19 +0xba fp=0xc000031f50 sp=0xc000031ed8 pc=0x5addda
runtime.main()
/usr/lib/go-1.22/src/runtime/proc.go:271 +0x29d fp=0xc000031fe0 sp=0xc000031f50 pc=0x43b55d
runtime.goexit({})
/usr/lib/go-1.22/src/runtime/asm_amd64.s:1695 +0x1 fp=0xc000031fe8 sp=0xc000031fe0 pc=0x46b0e1
goroutine 2 gp=0xc000006c40 m=nil [force gc (idle)]:
runtime.gopark(0x0?, 0x0?, 0x0?, 0x0?, 0x0?)
/usr/lib/go-1.22/src/runtime/proc.go:402 +0xce fp=0xc000074fa8 sp=0xc000074f88 pc=0x43b98e
runtime.goparkunlock(...)
/usr/lib/go-1.22/src/runtime/proc.go:408
runtime.forcegchelper()
/usr/lib/go-1.22/src/runtime/proc.go:326 +0xb3 fp=0xc000074fe0 sp=0xc000074fa8 pc=0x43b813
runtime.goexit({})
/usr/lib/go-1.22/src/runtime/asm_amd64.s:1695 +0x1 fp=0xc000074fe8 sp=0xc000074fe0 pc=0x46b0e1
created by runtime.init.6 in goroutine 1
/usr/lib/go-1.22/src/runtime/proc.go:314 +0x1a
goroutine 3 gp=0xc000007180 m=nil [GC sweep wait]:
runtime.gopark(0x0?, 0x0?, 0x0?, 0x0?, 0x0?)
/usr/lib/go-1.22/src/runtime/proc.go:402 +0xce fp=0xc000075780 sp=0xc000075760 pc=0x43b98e
runtime.goparkunlock(...)
/usr/lib/go-1.22/src/runtime/proc.go:408
runtime.bgsweep(0xc0000240e0)
/usr/lib/go-1.22/src/runtime/mgcsweep.go:278 +0x94 fp=0xc0000757c8 sp=0xc000075780 pc=0x426cf4
runtime.gcenable.gowrap1()
/usr/lib/go-1.22/src/runtime/mgc.go:203 +0x25 fp=0xc0000757e0 sp=0xc0000757c8 pc=0x41b845
runtime.goexit({})
/usr/lib/go-1.22/src/runtime/asm_amd64.s:1695 +0x1 fp=0xc0000757e8 sp=0xc0000757e0 pc=0x46b0e1
created by runtime.gcenable in goroutine 1
/usr/lib/go-1.22/src/runtime/mgc.go:203 +0x66
goroutine 4 gp=0xc000007340 m=nil [GC scavenge wait]:
runtime.gopark(0xc0000240e0?, 0x657100?, 0x1?, 0x0?, 0xc000007340?)
/usr/lib/go-1.22/src/runtime/proc.go:402 +0xce fp=0xc000075f78 sp=0xc000075f58 pc=0x43b98e
runtime.goparkunlock(...)
/usr/lib/go-1.22/src/runtime/proc.go:408
runtime.(*scavengerState).park(0x797520)
/usr/lib/go-1.22/src/runtime/mgcscavenge.go:425 +0x49 fp=0xc000075fa8 sp=0xc000075f78 pc=0x4246e9
runtime.bgscavenge(0xc0000240e0)
/usr/lib/go-1.22/src/runtime/mgcscavenge.go:653 +0x3c fp=0xc000075fc8 sp=0xc000075fa8 pc=0x424c7c
runtime.gcenable.gowrap2()
/usr/lib/go-1.22/src/runtime/mgc.go:204 +0x25 fp=0xc000075fe0 sp=0xc000075fc8 pc=0x41b7e5
runtime.goexit({})
/usr/lib/go-1.22/src/runtime/asm_amd64.s:1695 +0x1 fp=0xc000075fe8 sp=0xc000075fe0 pc=0x46b0e1
created by runtime.gcenable in goroutine 1
/usr/lib/go-1.22/src/runtime/mgc.go:204 +0xa5
goroutine 18 gp=0xc000102700 m=nil [finalizer wait]:
runtime.gopark(0xc000074648?, 0x40f445?, 0xa8?, 0x1?, 0xc0000061c0?)
/usr/lib/go-1.22/src/runtime/proc.go:402 +0xce fp=0xc000074620 sp=0xc000074600 pc=0x43b98e
runtime.runfinq()
/usr/lib/go-1.22/src/runtime/mfinal.go:194 +0x107 fp=0xc0000747e0 sp=0xc000074620 pc=0x41a887
runtime.goexit({})
/usr/lib/go-1.22/src/runtime/asm_amd64.s:1695 +0x1 fp=0xc0000747e8 sp=0xc0000747e0 pc=0x46b0e1
created by runtime.createfing in goroutine 1
/usr/lib/go-1.22/src/runtime/mfinal.go:164 +0x3d
exit status 2
Appendices
This problem can also happen with ProvingKey.
Impact
Prover and verifier denial of service in case of maliciously crafted inputs (public key, verification key).
Patches
The issue is patched in https://github.com/Consensys/gnark/pull/1307. It was merged to gnark master at https://github.com/Consensys/gnark/commit/47ae846339add2bdf9983e499342bfdfe195191d. The fix will be incorporated in the next minor release of gnark (v0.11.1).
Workarounds
There are no convenient work-arounds currently. The best approach currently is to run key verification as a separate service which halts the verification pipeline in case of OOM when verification keys come from untrusted sources.
Latest trending attack
Criticalyesterday
Google Brotli decoder - Remote Code Execution via compressed requests (Exploitation Check)
This control is the second step of the Patrowl response to CVE-2026-111497 (Node2Shell). It complements the first control of 22 October 2026, which focused on the Node.js runtime, and does not replace it.
Why a second control
CVE-2026-111497 is an out-of-bounds write in the Google Brotli decoder, the library that decompresses Brotli ("br") data. It was first published as a Node.js vulnerability, because Node.js bundles this decoder. Later publications showed that the flaw is in the library itself. Every product that embeds an affected version of the decoder is concerned, whatever its language or vendor. A public proof of concept demonstrates code execution.
Any server that decompresses request bodies sent with "Content-Encoding: br" exposes the decoder to unauthenticated attackers. Known cases include Express 5 and NestJS 11 on Node.js, Koa and Fastify setups, Bun, Envoy and Istio with request decompression enabled, and any application or reverse proxy that decodes Brotli request bodies with an affected library.
The flaw also works in the other direction. A malicious server can compromise an unpatched client that decodes a Brotli response, for example Node.js fetch(), Python clients (requests, httpx, aiohttp, Scrapy) with the Brotli or brotlicffi package, or libcurl builds with Brotli support.
What this control checks
Patrowl sends small, valid Brotli-compressed requests to each asset and observes whether the server decodes them. The check does not depend on the technology: it detects the behaviour, whatever the stack behind it. These requests are what any legitimate client could send. They never reach the vulnerable code path and cannot affect the availability of the service.
How to read the result
Potentially impacted means the asset decodes Brotli request bodies: the attack surface is exposed. It does not confirm that the asset is vulnerable. The version of the Brotli decoder in use is not visible from the outside.
This check covers applications that parse request bodies on their root path. A Not impacted result does not rule out exposure on other routes, nor on the client side. Checking the versions on the servers remains the only exhaustive verification.
Affected and fixed versions
Google Brotli 1.0.3 to 1.2.0 are affected, fixed in 1.0.10, 1.1.1 and 1.2.1. Fixed releases of the main products embedding it: Node.js 22.23.4, 24.22.1 and 26.12.1 (end-of-life lines 20.x and older and 25.x receive no fix), Bun 1.4.4, Envoy 1.37.8, 1.38.6, 1.39.3 and 1.40.0, Istio 1.29.9, 1.30.6 and 1.31.2, Python Brotli 1.2.1 and brotlicffi 1.2.1.0. Products that link against the system library depend on the Brotli package of the Linux distribution.
Recommendations
Update every component that embeds the Brotli decoder (only real fix). Start with the assets flagged by this control. Restart the processes after the update. Rebuild containers, single-executable applications and appliances that bundle an affected runtime or library.
Reduce the exposure until the update is deployed. Reject requests with "Content-Encoding: br" at the reverse proxy, load balancer or WAF, case-insensitively and including lists such as "gzip, br". On Envoy and Istio, disable request decompression for Brotli.
Review outbound calls. List the features that fetch content from servers you do not control, and patch the services that host them first.
