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CVE-2026-109449

Symfony: Unbounded Nesting in the Expression Parser Lets Untrusted Expressions Crash the Process

8.7 HighFix available

In Symfony Expression Language versions prior to 5.4.54, 6.4.48, 7.4.21, and 8.1.9, the parser of the ExpressionLanguage component built its node tree with no bound on its depth. An expression made of tens of thousands of nested unary operators, array literals, binary operators or property accesses crashed the PHP process, while the tree was being freed.

#[Assert\ExpressionSyntax] passes the validated value to ExpressionLanguage::lint(), so an application validating expressions written by its users could be crashed by a single request, and so could any code parsing untrusted expressions.

This issue affects symfony/expression-language through v5.4.53, v6.0.0-BETA1 through v6.4.47, v7.0.0-BETA1 through v7.4.20, and v8.0.0-BETA1 through v8.1.8.

Attack profile

How easy it is to exploit

Attack vector
Network
Complexity
Low
Privileges needed
None
User interaction
None

What an attacker can affect

Confidentiality
None
Integrity
None
Availability
High

Exploit likelihood

0.38%Down 0.1 points since Oct 16, 2026
90%50%10%1%

What each source reports

CVE List Score used 8.7

Symfony: Unbounded Nesting in the Expression Parser Lets Untrusted Expressions Crash the Process

In Symfony Expression Language versions prior to 5.4.54, 6.4.48, 7.4.21, and 8.1.9, the parser of the ExpressionLanguage component built its node tree with no bound on its depth. An expression made of tens of thousands of nested unary operators, array literals, binary operators or property accesses crashed the PHP process, while the tree was being freed.

#[Assert\ExpressionSyntax] passes the validated value to ExpressionLanguage::lint(), so an application validating expressions written by its users could be crashed by a single request, and so could any code parsing untrusted expressions.

This issue affects symfony/expression-language through v5.4.53, v6.0.0-BETA1 through v6.4.47, v7.0.0-BETA1 through v7.4.20, and v8.0.0-BETA1 through v8.1.8.

Record
CVE-2026-109449
CVSS 4.0
8.7 HighCVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N
Weakness
CWE-674
Updated
2026-11-02
EUVDEUVD-2026-102134 8.7

In Symfony Expression Language versions prior to 5.4.54, 6.4.48, 7.4.21, and 8.1.9, the parser of the ExpressionLanguage component built its node tree with no bound on its depth. An expression made of tens of thousands of nested unary operators, array literals, binary operators or property accesses crashed the PHP process, while the tree was being freed.

#[Assert\ExpressionSyntax] passes the validated value to ExpressionLanguage::lint(), so an application validating expressions written by its users could be crashed by a single request, and so could any code parsing untrusted expressions.

This issue affects symfony/expression-language through v5.4.53, v6.0.0-BETA1 through v6.4.47, v7.0.0-BETA1 through v7.4.20, and v8.0.0-BETA1 through v8.1.8.

Record
EUVD-2026-102134
CVSS 4.0
8.7 HighCVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N
Updated
2026-11-02
NVD 8.7

In Symfony Expression Language versions prior to 5.4.54, 6.4.48, 7.4.21, and 8.1.9, the parser of the ExpressionLanguage component built its node tree with no bound on its depth. An expression made of tens of thousands of nested unary operators, array literals, binary operators or property accesses crashed the PHP process, while the tree was being freed.

#[Assert\ExpressionSyntax] passes the validated value to ExpressionLanguage::lint(), so an application validating expressions written by its users could be crashed by a single request, and so could any code parsing untrusted expressions.

This issue affects symfony/expression-language through v5.4.53, v6.0.0-BETA1 through v6.4.47, v7.0.0-BETA1 through v7.4.20, and v8.0.0-BETA1 through v8.1.8.

Record
CVE-2026-109449
CVSS 4.0
8.7 HighCVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X
Weakness
CWE-674
Updated
2026-11-02
OSV 8.7

Symfony: Unbounded Nesting in the Expression Parser Lets Untrusted Expressions Crash the Process

In Symfony Expression Language versions prior to 5.4.54, 6.4.48, 7.4.21, and 8.1.9, the parser of the ExpressionLanguage component built its node tree with no bound on its depth. An expression made of tens of thousands of nested unary operators, array literals, binary operators or property accesses crashed the PHP process, while the tree was being freed.

#[Assert\ExpressionSyntax] passes the validated value to ExpressionLanguage::lint(), so an application validating expressions written by its users could be crashed by a single request, and so could any code parsing untrusted expressions.

This issue affects symfony/expression-language through v5.4.53, v6.0.0-BETA1 through v6.4.47, v7.0.0-BETA1 through v7.4.20, and v8.0.0-BETA1 through v8.1.8.

Record
CVE-2026-109449
CVSS 4.0
8.7 HighCVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N
Weakness
CWE-674
Updated
2026-11-02
OSVDEBIAN-CVE-2026-109449 8.7

In Symfony Expression Language versions prior to 5.4.54, 6.4.48, 7.4.21, and 8.1.9, the parser of the ExpressionLanguage component built its node tree with no bound on its depth. An expression made of tens of thousands of nested unary operators, array literals, binary operators or property accesses crashed the PHP process, while the tree was being freed. #[Assert\ExpressionSyntax] passes the validated value to ExpressionLanguage::lint(), so an application validating expressions written by its users could be crashed by a single request, and so could any code parsing untrusted expressions. This issue affects symfony/expression-language through v5.4.53, v6.0.0-BETA1 through v6.4.47, v7.0.0-BETA1 through v7.4.20, and v8.0.0-BETA1 through v8.1.8.

Record
DEBIAN-CVE-2026-109449
CVSS 4.0
8.7 HighCVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X
Updated
2026-11-04
OSVUBUNTU-CVE-2026-109449 8.7

In Symfony Expression Language versions prior to 5.4.54, 6.4.48, 7.4.21, and 8.1.9, the parser of the ExpressionLanguage component built its node tree with no bound on its depth. An expression made of tens of thousands of nested unary operators, array literals, binary operators or property accesses crashed the PHP process, while the tree was being freed. #[Assert\ExpressionSyntax] passes the validated value to ExpressionLanguage::lint(), so an application validating expressions written by its users could be crashed by a single request, and so could any code parsing untrusted expressions. This issue affects symfony/expression-language through v5.4.53, v6.0.0-BETA1 through v6.4.47, v7.0.0-BETA1 through v7.4.20, and v8.0.0-BETA1 through v8.1.8.

Record
UBUNTU-CVE-2026-109449
CVSS 4.0
8.7 HighCVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N
Updated
2026-11-02

Affected products

Affected packages

Affected packages
PackageAffectedFixed
symfony
Debian:12
All versions, plus listed versions
5.4.23+dfsg-15.4.23+dfsg-1+deb12u15.4.23+dfsg-1+deb12u25.4.23+dfsg-1+deb12u35.4.23+dfsg-1+deb12u4
Show 45 moreShow less
5.4.23+dfsg-1+deb12u55.4.24+dfsg-15.4.25+dfsg-15.4.27+dfsg-15.4.28+dfsg-15.4.29+dfsg-15.4.30+dfsg-15.4.31+dfsg-15.4.31+dfsg-25.4.32+dfsg-15.4.33+dfsg-15.4.34+dfsg-15.4.34+dfsg-25.4.35+dfsg-15.4.35+dfsg-25.4.35+dfsg-35.4.52+dfsg-0+deb12u15.4.53+dfsg-0+deb12u16.3.0+dfsg-16.3.0~rc1+dfsg-16.3.0~rc2+dfsg-16.3.1+dfsg-16.3.3+dfsg-16.3.4+dfsg-16.3.5+dfsg-16.3.6+dfsg-16.3.7+dfsg-16.4.0+dfsg-16.4.0~beta2+dfsg-16.4.0~beta3+dfsg-16.4.0~rc1+dfsg-16.4.0~rc2+dfsg-16.4.1+dfsg-16.4.10+dfsg-16.4.11+dfsg-16.4.12+dfsg-16.4.13+dfsg-16.4.14+dfsg-16.4.15+dfsg-16.4.16+dfsg-16.4.16+dfsg-26.4.17+dfsg-16.4.17+dfsg-26.4.17+dfsg-36.4.17+dfsg-4
None known
symfony
Debian:13
before 6.4.49+dfsg-0+deb13u1, plus listed versions
6.4.21+dfsg-26.4.21+dfsg-2+deb13u16.4.24+dfsg-16.4.25+dfsg-16.4.40+dfsg-0+deb13u16.4.41+dfsg-0+deb13u1
6.4.49+dfsg-0+deb13u1
symfony
Debian:14
before 7.4.21+dfsg-1, plus listed versions
6.4.21+dfsg-26.4.24+dfsg-16.4.25+dfsg-17.0.4+dfsg-17.0.5+dfsg-1
Show 45 moreShow less
7.0.6+dfsg-17.0.7+dfsg-17.1.0~beta1+dfsg-17.1.0~rc1+dfsg-17.1.2+dfsg-17.1.3+dfsg-17.1.4+dfsg-17.1.5+dfsg-17.2.0~beta1+dfsg-17.2.0~beta2+dfsg-17.2.0~rc1+dfsg-17.2.1+dfsg-17.2.2+dfsg-17.2.3+dfsg-17.2.4+dfsg-17.2.5+dfsg-17.2.6-17.3.0+dfsg-17.3.0~beta1+dfsg-17.3.0~beta2+dfsg-17.3.0~rc1+dfsg-17.3.1+dfsg-17.3.2+dfsg-17.3.3+dfsg-17.3.4+dfsg-17.3.5-17.4.0+dfsg-17.4.0+dfsg-27.4.0~beta1-17.4.0~beta1-27.4.0~beta2+dfsg-17.4.0~beta2+dfsg-27.4.0~beta2+dfsg-37.4.0~rc1+dfsg-17.4.0~rc2+dfsg-17.4.0~rc3+dfsg-17.4.10+dfsg-17.4.12+dfsg-17.4.13+dfsg-17.4.13+dfsg-27.4.14+dfsg-17.4.15+dfsg-17.4.15+dfsg-27.4.16+dfsg-17.4.17+dfsg-1
7.4.21+dfsg-1
symfony
Ubuntu:16.04:LTS
All versions, plus listed versions
2.7.1+dfsg-12.7.5+dfsg-12.7.9+dfsg-12.7.9+dfsg-1ubuntu22.7.10-0ubuntu2
None known
symfony
Ubuntu:Pro:18.04:LTS
All versions, plus listed versions
2.8.7+dfsg-1.3ubuntu13.4.3+dfsg-1ubuntu43.4.6+dfsg-13.4.6+dfsg-1ubuntu0.13.4.6+dfsg-1ubuntu0.1+esm13.4.6+dfsg-1ubuntu0.1+esm2
None known
symfony
Ubuntu:Pro:20.04:LTS
All versions, plus listed versions
4.3.4+dfsg-1ubuntu14.3.8+dfsg-1ubuntu14.3.8+dfsg-1ubuntu1+esm14.3.8+dfsg-1ubuntu1+esm2
None known
symfony
Ubuntu:Pro:22.04:LTS
All versions, plus listed versions
5.2.6+dfsg-1ubuntu75.4.4+dfsg-1ubuntu85.4.4+dfsg-1ubuntu8+esm1
None known
symfony
Ubuntu:Pro:24.04:LTS
All versions, plus listed versions
5.4.23+dfsg-1ubuntu15.4.35+dfsg-3ubuntu16.4.5+dfsg-3ubuntu26.4.5+dfsg-3ubuntu36.4.5+dfsg-3ubuntu3+esm1
None known
symfony
Ubuntu:26.10
All versions, plus listed versions
7.4.7+dfsg-1ubuntu17.4.9+dfsg-1ubuntu17.4.13+dfsg-2ubuntu17.4.14+dfsg-1ubuntu27.4.15+dfsg-2ubuntu27.4.16+dfsg-1ubuntu2
None known
symfony
Ubuntu:26.04:LTS
All versions, plus listed versions
6.4.24+dfsg-17.4.5+dfsg-1ubuntu17.4.6+dfsg-2ubuntu17.4.7+dfsg-1ubuntu1
None known

History

History
RecordedChangedSources
affected, factsOSV
first indexedCVE List, EUVD, NVD, OSV

Dates are when Every CVE recorded each change. Upstream dates may differ.

In short

CVE-2026-109449 is a high vulnerability (CVSS 8.7) in Sensiolabs Symfony, published October 15, 2026. No source lists public exploit code. EPSS puts the chance of exploitation in the next 30 days at 0.38%, the 31st percentile. Fixed in symfony 6.4.49+dfsg-0+deb13u1.

References

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