What is CVE-2026-109413?

CVE-2026-109413 is a high-severity security vulnerability in symfony/symfony (composer), affecting versions >= 2.0.0, < 5.4.54. It is fixed in 5.4.54, 6.4.45, 7.4.18, 8.1.6.

Which packages are affected by CVE-2026-109413?

symfony/symfony (composer) versions >= 2.0.0, = 2.0.0, < 5.4.54.

Is there a fix for CVE-2026-109413?

Yes. CVE-2026-109413 is fixed in 5.4.54, 6.4.45, 7.4.18, 8.1.6. Upgrade to this version or later.

Is CVE-2026-109413 exploitable, and should I be worried?

Whether CVE-2026-109413 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk.

What actually determines whether CVE-2026-109413 is exploitable, and how bad it is?

Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.

CVE-2026-109413 in symfony/symfony

Q: Which packages are affected by CVE-2026-109413?

symfony/symfony (composer) versions >= 2.0.0, = 2.0.0, < 5.4.54.

Q: Is there a fix for CVE-2026-109413?

Yes. CVE-2026-109413 is fixed in 5.4.54, 6.4.45, 7.4.18, 8.1.6. Upgrade to this version or later.

Q: Is CVE-2026-109413 exploitable, and should I be worried?

Whether CVE-2026-109413 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk.

Q: What actually determines whether CVE-2026-109413 is exploitable, and how bad it is?

Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.

Q: How do I fix CVE-2026-109413?

Upgrade: symfony/symfony to 5.4.54 or later, symfony/symfony to 6.4.45 or later, symfony/symfony to 7.4.18 or later, symfony/symfony to 8.1.6 or later, symfony/yaml to 5.4.54 or later, symfony/yaml to 6.4.45 or later, symfony/yaml to 7.4.18 or later, symfony/yaml to 8.1.6 or later.

Summary

Symfony: Unbounded Recursion in the YAML Inline Lexer Lets a Single Document Crash the Process

Description

Yaml\Parser::lexInlineStructure() recursed through lexInlineMapping() and lexInlineSequence() for every { and [ of an inline collection, without entering the nesting level that the rest of the parser bounds with maxNestingLevel. A document made of deeply nested inline collections, such as [[[[...]]]], exhausted the stack while it was being lexed: depending on the PHP version and its stack settings, the process crashed or the request ended with a fatal error.

Any code parsing untrusted YAML is affected. That includes #[MapRequestPayload] when the Yaml component is installed and the endpoint does not restrict acceptFormat: a single unauthenticated request with a YAML content type is enough.

Resolution

The inline lexer now enters and leaves the same nesting level as the rest of the parser, so nested inline collections are bounded by maxNestingLevel, and the parser raises a ParseException beyond it.

The patches for this issue are available here for branch 5.4 (and forward-ported to 6.4, 7.4, 8.1 and 8.2).

Credits

We would like to thank Nicolas Grekas for reporting the issue and providing the fix.

References

Fix: #65688

Impact

Affected versions

symfony/symfony (>= 2.0.0, < 5.4.54) symfony/symfony (>= 6.0.0, < 6.4.45) symfony/symfony (>= 7.0.0, < 7.4.18) symfony/symfony (>= 8.0.0, < 8.1.6) symfony/yaml (>= 2.0.0, < 5.4.54) symfony/yaml (>= 6.0.0, < 6.4.45) symfony/yaml (>= 7.0.0, < 7.4.18) symfony/yaml (>= 8.0.0, < 8.1.6)

Security releases

symfony/symfony → 5.4.54 (composer) symfony/symfony → 6.4.45 (composer) symfony/symfony → 7.4.18 (composer) symfony/symfony → 8.1.6 (composer) symfony/yaml → 5.4.54 (composer) symfony/yaml → 6.4.45 (composer) symfony/yaml → 7.4.18 (composer) symfony/yaml → 8.1.6 (composer)

Kodem intelligence

Severity tells you how bad this could be in the worst case. It does not tell you whether you are exposed. Exploitability and impact are functions of runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A vulnerable package can sit in your dependency tree and never run.

Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter. Kodem's runtime-powered SCA identifies whether this CVE is reachable in your applications.

Already deployed Kodem?

See it in your environment New to Kodem? Get a demo →

Remediation advice

Upgrade the following packages to resolve this vulnerability:

symfony/symfony to 5.4.54 or later; symfony/symfony to 6.4.45 or later; symfony/symfony to 7.4.18 or later; symfony/symfony to 8.1.6 or later; symfony/yaml to 5.4.54 or later; symfony/yaml to 6.4.45 or later; symfony/yaml to 7.4.18 or later; symfony/yaml to 8.1.6 or later

Kodem Kai can prioritize this vulnerability in your dependency tree and generate a fix recommendation.

Frequently Asked Questions

What is CVE-2026-109413? CVE-2026-109413 is a high-severity security vulnerability in symfony/symfony (composer), affecting versions >= 2.0.0, < 5.4.54. It is fixed in 5.4.54, 6.4.45, 7.4.18, 8.1.6.
Which packages are affected by CVE-2026-109413?
- symfony/symfony (composer) (versions >= 2.0.0, < 5.4.54)
- symfony/yaml (composer) (versions >= 2.0.0, < 5.4.54)
Is there a fix for CVE-2026-109413? Yes. CVE-2026-109413 is fixed in 5.4.54, 6.4.45, 7.4.18, 8.1.6. Upgrade to this version or later.
Is CVE-2026-109413 exploitable, and should I be worried? Whether CVE-2026-109413 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
What actually determines whether CVE-2026-109413 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
How do I fix CVE-2026-109413?
- Upgrade symfony/symfony to 5.4.54 or later
- Upgrade symfony/symfony to 6.4.45 or later
- Upgrade symfony/symfony to 7.4.18 or later
- Upgrade symfony/symfony to 8.1.6 or later
- Upgrade symfony/yaml to 5.4.54 or later
- Upgrade symfony/yaml to 6.4.45 or later
- Upgrade symfony/yaml to 7.4.18 or later
- Upgrade symfony/yaml to 8.1.6 or later

Other vulnerabilities in symfony/symfony

CVE-IDSeverityPackage summary

CVE-2026-108082Highsymfony/http-foundation: Symfony: ReDoS in HeaderUtils::split() Reachable Through the Cache-Control Request Header CVE-2026-48784Mediumsymfony/routing: Symfony: UrlGenerator Dot-Segment Encoding Skips Every Other Chained `../` or `./` → Generated URL Collapses Off-Route Under RFC 3986…CVE-2026-48760Mediumsymfony/html-sanitizer: Symfony: HtmlSanitizer URL Parser Deny Gates Underinclusive: Percent-Encoded BiDi Marks and Unicode Whitespace Bypass Visual-Spoofing…CVE-2026-48747Mediumsymfony/mailomat-mailer: Symfony: Mailomat Mailer Webhook Parser Reads the HMAC Algorithm from the Request: Signature Algorithm Downgrade CVE-2026-48736Mediumsymfony/http-client: Symfony: IpUtils::PRIVATE_SUBNETS Omits IPv6 Transition Forms (6to4, NAT64, Teredo, IPv4-compatible): SSRF Bypass in…