CVE-2026-123792: sensiolabs symfony · Inefficient Algorithmic Complexity
Affects sensiolabs symfonySource CVE Database V5
Not known to be exploited · CVSS 8.7 High · fixed in 8.1.11 : patch sensiolabs symfony soon.
Data as of 6 Nov 2026, 15:47 UTC
Thin evidence
One scorer or none| CNA (Checkmarx) | CVSS 4.0 | 8.7 |
|---|
- Patch
- Available – fixed in 8.1.11, 7.4.23, 6.4.50 +1
CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:NExploitation evidence
Disclosed: evidence found.
CVE published 6 Nov 2026
Detectable: no evidence on record.
No public nuclei template indexed
Weaponized: no evidence on record.
No public exploit code indexed in Metasploit or Exploit-DB
Exploited in the wildExploited: no evidence on record.
Not in CISA KEV and no source reports exploitation
Observed by OffSeq MirageSeen by Mirage: no evidence on record.
No attack traffic recorded by OffSeq Mirage sensors
A missing step is not evidence of safety. Sources: cve.org (opens in a new tab), the Metasploit, Exploit-DB and nuclei-templates index as of 6 Nov 2026.
What to do
Upgrade symfony and symfony/yaml to 8.1.11, 7.4.23, 6.4.50 or 5.4.56.
Affected software
| Product | Affected | Fixed in |
|---|---|---|
| symfonysymfony/yaml | Affected
| Fixed in
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| symfonysymfony/yaml | Affected
| Fixed in
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| symfonysymfony/yaml | Affected
| Fixed in
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| symfonysymfony/yaml | Affected
| Fixed in
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Packagistsymfony/yamlpkg:composer/symfony/yamlOther threats | Affected
| Fixed in
|
Check your own hosts for these packages with threat-finder (opens in a new tab), our free open-source scanner.
AI-suggested
Fixed versions are available: upgrade Symfony to 5.4.56, 6.4.50, 7.4.23, or 8.1.11 or later. Applying these official fixes will resolve the inefficient parsing issue. Until upgraded, restrict or validate YAML input sources, especially for untrusted data. In Symfony 7.4 and later, restrict acceptFormat or disable YAML request payload mapping where possible to reduce exposure. No other vendor advisory mitigation instructions are provided.
Description
CVE-2026-123792 is an inefficient algorithmic complexity vulnerability in the Symfony Yaml component affecting versions prior to 5.4.56, 6.4.50, 7.4.23, and 8.1.11. The vulnerability causes the YAML parser to perform excessive repeated work when processing certain crafted YAML documents, leading to exponential or quadratic parsing time growth. This can keep a PHP process busy for extended periods, potentially causing denial of service. The issue affects any code parsing untrusted YAML with default flags, including some Symfony request payload mappings that accept YAML input without restrictions. The vulnerability is rated high severity with a CVSS 4.0 score of 8.7.
References
- github.com/symfony/symfony/security/advisories/GHSA-hwfg-qwvh-2wfx (opens in a new tab)
- github.com/symfony/symfony/commit/487f63bf2cacebc8ed8273c5c10d92955acd2402 (opens in a new tab)
- github.com/symfony/symfony/commit/08db22d52e5d3e6ec2f5c50db30a4d818100ffb9 (opens in a new tab)
- github.com/symfony/symfony/commit/49e03035eda3000e978a4612db74900013255ccd (opens in a new tab)