The fb_unserialize function did not impose a depth limit for nested deserialization. That meant a maliciously constructed string could cause deserialization to recurse, leading to stack exhaustion. This issue affected HHVM prior to v4.32.3, between versions 4.33.0 and 4.56.0, 4.57.0, 4.58.0, 4.58.1, 4.59.0, 4.60.0, 4.61.0, 4.62.0.
An official patch is available. Apply the patch as soon as possible.
CVSS v4.0 Metrics
Exploitability
Attack VectorNetwork
ComplexityLow
RequirementsPresent
PrivilegesNone
User InteractionNone
Threat
Exploit MaturityUnreported
Vulnerable System
ConfidentialityNone
IntegrityNone
AvailabilityHigh
Subsequent System
ConfidentialityNone
IntegrityNone
AvailabilityNone
Supplemental
SafetyNegligible
AutomatableYes
RecoveryAutomatic
Value DensityConcentrated
UrgencyMedium
Patch StatusOfficial Patch
Change Log
| Date | Source | Changes | Score |
|---|
| 2026-07-21 | nvd | AV: P→N, AC: H→L, PR: H→N, UI: A→N, VA: N→H | 0.0 → 4.6 |
| 2026-07-21 | nvd | patch: Unavailable→Official Patch | 0.0 → 0.0 |
| 2026-07-21 | cve.org | initial, patch: Unavailable | 0.0 |
Affected Software
| Vendor | Product | Version |
|---|
| Facebook | HHVM | < 4.32.3 |
| facebook | hhvm | < 4.32.3 |
| facebook | hhvm | ≥ 4.33.0, < 4.56.1 |
| Facebook | HHVM | 4.32.3 |
| Facebook | HHVM | 4.33.0 |
| Facebook | HHVM | 4.56.1 |
| facebook | hhvm | 4.57.0 |
| Facebook | HHVM | 4.57.0 |
| Facebook | HHVM | 4.57.1 |
| facebook | hhvm | 4.58.0 |
| Facebook | HHVM | 4.58.0 |
| facebook | hhvm | 4.58.1 |
| Facebook | HHVM | 4.58.2 |
| Facebook | HHVM | 4.59.0 |
| facebook | hhvm | 4.59.0 |
| Facebook | HHVM | 4.59.1 |
| Facebook | HHVM | 4.60.0 |
| facebook | hhvm | 4.60.0 |
| Facebook | HHVM | 4.60.1 |
| facebook | hhvm | 4.61.0 |
| Facebook | HHVM | 4.61.0 |
| Facebook | HHVM | 4.61.1 |
| Facebook | HHVM | 4.62.0 |
| facebook | hhvm | 4.62.0 |
| Facebook | HHVM | 4.62.1 |
Published: 2021-03-11
