8.7

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

Analyzed
Published 25-05-2026Last modified 27-05-2026

Vulnerability summary

CVE-2026-47066 is a high (CVSS 8.7) Loop with Unreachable Exit Condition vulnerability in benoitc hackney. EPSS estimates a 0.75% chance of exploitation in the next 30 days, higher than 55.1% of scored vulnerabilities. 1 public exploit is recorded.

Priority
Prioritisepublic exploit

Public exploit (GitHub, Date unknown)

Source freshness unavailable

How is this decided?
CVSS score
8.7/10
010
High · v4.0 (CVE.org)
EPSS score
0.75%
0%100%
Low · +0.05 pp in 30 days
KEVNot listedNot listed by any tracked catalog.
RansomwareNot flaggedNo ransomware use recorded.
Public exploits1github

Timeline

  1. 25-05-2026
    PublishedVulnerability first disclosed.
  2. 27-05-2026
    Last modifiedVulnerability information updated.

Description

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.

CVSS metrics

3 scores · 2 sources · 2 versions

EPSS trend

Probability

0.75%

Chance of exploitation in the next 30 days

Percentile

55%

Versus all other CVEs

30-day change

Increase +0.05 pp

From 0.70% on 04-10-2026

04-10-202603-11-2026

Known exploited

Compare KEV catalogs
CISA KEV

Not in the CISA KEV catalog.

ENISA CNW

Not in the ENISA CNW catalog.

CIRCL

Not in the CIRCL catalog.

Public exploits

1 found
  • githubUnverified

    Hackney

    Maturity: poc

Weaknesses

CWE · root cause

Affected systems

Version check

Known conditions: network-reachable, no authentication, no user interaction (CVSS vector). Other conditions: not stated in public data.

Benoitc1 product
  • hackney≥ 2.0.0-beta.1, < 4.0.1 | ≥ 408e5fe20302226ea8c74dde2bcbd452d712b5b2, < e548aba1f97ffa3f4750da7b772998fb78c01894 | ≥ 2.0.0, < 4.0.1

1 vendor · 1 product

References

4 links