The unserialize() function supported a type code, "S", which was meant to be supported only for APC serialization. This type code allowed arbitrary memory addresses to be accessed as if they were static StringData objects. 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
ConfidentialityHigh
IntegrityNone
AvailabilityNone
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, VC: 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
