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NVD / CVE Program· CNA EEF

CVE-2026-47066: Infinite loop in Alt-Svc header parser in hackney

Noroxi assessment

Priority: Monitor (action score 34/100)

  • 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: 0.75% (FIRST EPSS); higher than 55.3% 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.
  • According to CISA the attack is automatable: targets can be found by mass scanning.
  • Fixed version: benoitc hackney 4.0.1, e548aba1f97ffa3f4750da7b772998fb78c01894.

Low priority for now. Upgrade to benoitc hackney 4.0.1, e548aba1f97ffa3f4750da7b772998fb78c01894 or later.

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

Loop with Unreachable Exit Condition ('Infinite Loop') vulnerability in benoitc hackney allows Excessive Allocation. The Alt-Svc response header parser in src/hackney_altsvc.erl does not guarantee forward progress. When parse_token/2 receives a non-token, non-whitespace, non-comma byte (e.g. !, @, =, ;), it returns the input unchanged. skip_comma/1 also returns the buffer unchanged when the first byte is not a comma. parse_entries/2 then recurses with identical data, creating a tight infinite tail-recursive loop that pins a scheduler at 100% CPU. The calling process never returns. The entry point parse_and_cache/3 is called synchronously in the connection process on every HTTP response. A single-byte Alt-Svc: ! response header is sufficient to trigger the hang; the header is fully controlled by any HTTP origin the client connects to. This issue affects hackney: from 2.0.0-beta.1 before 4.0.1.

HighCVSS 8.7 · v4.0—No exploit Fix available
Published
May 25, 2026
Updated
Jul 24, 2026
EPSS
0.7% · 55th percentile

Report tools

JSON

Action score

34

Monitor

Low priority for now.

CVSS
34 / 40 · 8.7 / 10
CISA KEV
0 / 30 · Not listed
EPSS
0 / 30 · 0.7%

CISA SSVC decision

Exploitation
proof of concept
Automatable
yes
Technical impact
partial

Vulnrichment: CISA's decision-tree inputs.

CNA vs NVD score

NVD
—
CNA · EEF
8.7
NVD has not scored this yet; the score shown is the CNA’s.

CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N

The score given by the assigning authority versus NVD’s independent score. A gap means the severity is contested.

Get told when this record changes

  • Not in KEV: no record of exploitation in the wild
  • No public exploit code on record
  • A fix has been released

If any of these changes, we'll tell you in the daily email digest.

Follow CVE-2026-47066

When you'll hear from us

  • when it enters CISA KEV
  • when exploit code appears or is weaponized
  • when the record is updated (including a fixed version)
  • when EPSS rises 20 points in a week

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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.

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Affected 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.

VendorProduct
benoitchackney

Affected versions

NVD version ranges (for catalog products). Add the product to your stack with a version and matching uses these.

  • benoitc hackney2.0.0 and later · before 4.0.1

Versions reported by the vendor

Affected version ranges reported by the assigning authority (EEF). Independent of NVD's CPE analysis and usually ahead of it.

  • benoitc hackney

    • 2.0.0-beta.1 and later · before 4.0.1affected · semver
    • 408e5fe20302226ea8c74dde2bcbd452d712b5b2 and later · before e548aba1f97ffa3f4750da7b772998fb78c01894affected · git

Package-level exposure

OSV and GitHub Advisory data: ecosystem, package and range. SBOM matching uses this table.

EcosystemPackageAffected rangeFix
Hexhackneyfrom 2.0.0 · before 4.0.14.0.1
Hexhackneyfrom 2.0.0-beta.1 · before 4.0.14.0.1

Same product

benoitc: all records

Other highest-scoring records for the same primary product.

  • CVE-2026-115693Custom cacerts or cacertfile do not restrict trust to the pinned CA in hackney
    36Monitor
  • CVE-2026-47073Unbounded memory consumption in WebSocket client in hackney
    34Monitor
  • CVE-2026-47067Atom table exhaustion via unrecognized URL schemes in hackney
    34Monitor

Published before and after this one in the same product

  • Later →CVE-2026-47069May 25, 2026 · CRLF injection in cookie domain/path options in hackney
    8Monitor
  • Later →CVE-2026-47070May 25, 2026 · HTTP/3 redirect handler leaks Authorization and Cookie headers to cross-origin redirect target in hackney
    24Monitor
  • Later →CVE-2026-47071May 25, 2026 · SOCKS5 TLS upgrade ignores caller timeout in hackney
    32Monitor

Remediation

Which version to upgrade to

Fix versions compiled from the vendor, package registries and Microsoft. Verify the vendor's note before upgrading.

Product / packageFixed versionSource
benoitc hackney4.0.1Vendor (CNA)
benoitc hackneye548aba1f97ffa3f4750da7b772998fb78c01894Vendor (CNA)
Hex:hackney4.0.1Package registry (OSV)

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.

No history yet (it accumulates with the daily EPSS job).

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 researchers

Finders, reporters and analysts named in the CNA record. Click a name for that researcher’s other records.

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
Integrity
Availability
Attack vector
Network
Attack complexity
Low
Privileges required
None
User interaction
None
Scope
X

Weakness class (CWE)

CWE-835 · Loop with Unreachable Exit Condition ('Infinite Loop')

CVSS vector

CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X

nvd-secondary

Attack context

MITRE CAPEC attack patterns and ATT&CK techniques for this weakness class (CWE). A starting point for detection rules and threat hunting.

MITRE has no CAPEC/ATT&CK mapping for this CWE.

Change log

  1. Fix✗ → ✓

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References

Show all references (2 more)

Vendor advisories and official records. Exploit/PoC links are deliberately left out.

All records