CVE-2026-45133
Crafted YAML causes Symfony parser to recurse and crash workers (Denial of Service).
Is CVE-2026-45133 being exploited?
Not confirmed. CVE-2026-45133 does not appear in CISA's Known Exploited Vulnerabilities catalog, which records only exploitation that has been observed and reported publicly. That is evidence of absence of a report, not evidence the flaw is unattacked. EPSS currently estimates a 0.63% probability of exploitation in the next 30 days.
How severe is CVE-2026-45133?
CVE-2026-45133 is rated High with a CVSS score of 8.2. Severity describes how bad exploitation would be, not how likely it is: pair it with exploitation evidence before deciding what to patch first.
Is there a patch for CVE-2026-45133?
Yes. A fix has been recorded for CVE-2026-45133. The vendor advisory is the authority on the exact fixed version — apply it from there rather than from a summary.
What does CVE-2026-45133 affect?
CVE-2026-45133 affects Symfony YAML parser in apps using Symfony versions <5.4.52, Symfony YAML parser in apps using Symfony versions <6.4.40, Symfony YAML parser in apps using Symfony versions <7.4.12, Symfony YAML parser in apps using Symfony versions <8.0.12. Confirm the exact affected versions against the vendor advisory before deciding you are exposed.
What should I do about CVE-2026-45133?
Upgrade to 5.4.52 / 6.4.40 / 7.4.12 / 8.0.12 and validate untrusted YAML
Exploitation status reflects CISA's KEV catalog as we last synced it. Check the catalog directly.
Attacker-controlled YAML with deep nesting triggers unbounded parser recursion, exhausting PHP stack and crashing worker processes (remote DoS).
Immediate action required
- affected< 5.4.52
- affected>= 6.0.0-BETA1 and < 6.4.40
- affected>= 7.0.0-BETA1 and < 7.4.12
- affected>= 8.0.0-BETA1 and < 8.0.12
As published in the CVE Program record. A version outside these ranges is not a statement that it is unaffected — vendors sometimes understate a range, and distribution-backported builds carry upstream numbers that do not reflect what was patched into them.