CVE-2020-1899: The unserialize() function supported a type code, "S", which was meant to be supported only for APC serialization.
Noroxi assessment
Priority: Monitor (action score 30/100)
- The sources we track (CISA KEV, Exploit-DB, Metasploit, Nuclei, GitHub) show no public exploit code or exploitation in the wild.
- Probability of exploitation in the next 30 days: 1.2% (FIRST EPSS); higher than 68.4% of all records.
- Anyone who can reach it over the internet can trigger it. No account or password is required. No user action is required. No special conditions are required; it is repeatable.
- No fixed version is recorded, but the references include a patch (commit or PR) link.
Low priority for now. See the fix and affected versions sections below.
Generated automatically from the record's data: CVSS (NVD and CNA), CISA KEV and SSVC, FIRST EPSS, exploit sources, fixed versions. How we calculate it
Primary sources: NVD · CVE.org · FIRST EPSS
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.
- Published
- Mar 10, 2021
- Updated
- Jun 16, 2026
- EPSS
- 1.2% · 68th percentile
- CWE
- CWE-822
Report tools
Action score
30
Monitor
Low priority for now.
- CVSS
- 30 / 40 · 7.5 / 10
- CISA KEV
- 0 / 30 · Not listed
- EPSS
- 0 / 30 · 1.2%
Get told when this record changes
- Not in KEV: no record of exploitation in the wild
- No public exploit code on record
- No fixed version yet
If any of these changes, we'll tell you in the daily email digest.
Running WordPress? Scan your site free with WP Lens
Noroxi analysis
What does it mean in your environment?
The assessment above is generated automatically from the record's data; it doesn't know your environment. Our team verifies on your systems whether this vulnerability is actually exploitable and which mitigation is enough.
We use this product, ask for helpAffected systems
Is your version affected?
Pick the product and type the version you run. It's compared with this record's version ranges in your browser; the version isn't sent anywhere.
| Vendor | Product | CPE |
|---|---|---|
| hhvm | cpe:2.3:a:facebook:hhvm |
Affected versions
NVD version ranges (for catalog products). Add the product to your stack with a version and matching uses these.
- facebook hhvmbefore 4.32.3
- facebook hhvm4.33.0 and later · before 4.56.1
- facebook hhvm4.57.0
- facebook hhvm4.58.0
- facebook hhvm4.58.1
- facebook hhvm4.59.0
- facebook hhvm4.60.0
- facebook hhvm4.61.0
- facebook hhvm4.62.0
Versions reported by the vendor
Affected version ranges reported by the assigning authority (facebook). Independent of NVD's CPE analysis and usually ahead of it.
Facebook HHVM
- 4.62.0, 4.61.0, 4.60.0, 4.59.0, 4.57.0affected
- 4.62.1 and later · before unspecifiednot affected
- 4.61.1 and later · before unspecifiednot affected
- 4.60.1 and later · before unspecifiednot affected
- 4.59.1 and later · before unspecifiednot affected
- 4.58.2 and later · before unspecifiednot affected
- 4.58.0 and later · before unspecifiedaffected
- 4.57.1 and later · before unspecifiednot affected
- 4.56.1 and later · before unspecifiednot affected
- 4.33.0 and later · before unspecifiedaffected
Same product
facebook: all recordsOther highest-scoring records for the same primary product.
- CVE-2019-11930An invalid free in mb_detect_order can cause the application to crash or potentially result in remote code execution.40Plan
- CVE-2019-11929Insufficient boundary checks when formatting numbers in number_format allows read/write access to out-of-bounds memory, potentially leading 40Plan
- CVE-2019-11926Insufficient boundary checks when processing M_SOFx markers from JPEG headers in the GD extension could allow access to out-of-bounds memory40Plan
Published before and after this one in the same product
- ← EarlierCVE-2021-24025Mar 10, 2021 · Due to incorrect string size calculations inside the preg_quote function, a large input string passed to the function can trigger an integer39Monitor
- ← EarlierCVE-2020-1898Mar 10, 2021 · The fb_unserialize function did not impose a depth limit for nested deserialization.30Monitor
- Later →CVE-2020-1900Mar 10, 2021 · When unserializing an object with dynamic properties HHVM needs to pre-reserve the full size of the dynamic property array before inserting 39Monitor
Remediation
Which version to upgrade to
Fix versions compiled from the vendor, package registries and Microsoft. Verify the vendor's note before upgrading.
No fix version is recorded for this entry. Check the references for vendor advisories.
Exploit status
No known public exploit
No public exploit has been observed yet. That doesn't mean you're safe, only that the bar is a little higher.
Research context
For pentesters and researchers: attack profile, score disagreement, timeline, patch commits, credits, variant and chain candidates, bug bounty scope. All derived from existing data; no exploit code.
Timeline
From publication to today: proof of concept, Metasploit module, CISA KEV and fix record. Dates are as reported by the sources.
No dated events beyond publication.
FIRST EPSS daily score; only changes of 0.01 or more are recorded (step chart).
Patch and commit links
Commit, PR and diff links among the references. A starting point for patch-diffing and variant hunting; fixes, not exploits.
Credits
All researchersFinders, reporters and analysts named in the CNA record. Click a name for that researcher’s other records.
No credits in the CNA record.
Variant candidates
Same product, same weakness class, within 18 months. If the patch missed the root cause, the sibling bug is here.
No nightly-computed relations.
Chain candidates
An authentication bypass and a privilege-requiring bug in the same product, published close together: combined they may become an unauthenticated path.
—
Bug bounty scope
No known public program.
Source: bounty-targets-data (public HackerOne, Bugcrowd, Intigriti, YesWeHack listings).
Technical details
Attack conditions
- Anyone who can reach it over the internet can trigger it.
- No account or password is required.
- No user action is required.
- No special conditions are required; it is repeatable.
If successful
- Confidentiality
- high · data can be read
- Integrity
- none
- Availability
- none
- Attack vector
- Network
- Attack complexity
- Low
- Privileges required
- None
- User interaction
- None
- Scope
- Unchanged
- Confidentiality impact
- High
- Integrity impact
- None
- Availability impact
- None
Weakness class (CWE)
CWE-822 · Untrusted Pointer DereferenceCVSS vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N
nvd-primary
Attack context
MITRE CAPEC attack patterns and ATT&CK techniques for this weakness class (CWE). A starting point for detection rules and threat hunting.
Attack patterns (CAPEC)
ATT&CK techniques
—
Change log
No changes recorded on tracked fields yet. Score, KEV, exploit maturity and fix status changes appear here.
References
Show all references (1 more)Show less
Vendor advisories and official records. Exploit/PoC links are deliberately left out.