How severe is CVE-2026-47077?

No CVSS score has been assigned to CVE-2026-47077 yet. Review the advisory details and affected package list to assess your exposure.

Which packages are affected by CVE-2026-47077?

CVE-2026-47077 affects the following packages: hackney (Hex). Ecosystems affected: Hex.

How do I fix CVE-2026-47077?

Update hackney to 4.0.1 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-47077 is resolved across your whole dependency graph.

How do I detect CVE-2026-47077 in my Hex dependencies?

Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for hackney, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.

How do I mitigate CVE-2026-47077 if there is no patch (or I can't update yet)?

Cap what an attacker can consume: apply request size, rate and timeout limits in front of the affected component, and run it with memory and CPU limits so exhaustion degrades one worker rather than the whole service.

Is CVE-2026-47077 actively exploited in the wild?

No public exploit code has been indexed for CVE-2026-47077 yet. This does not mean the vulnerability cannot be exploited — absence of public exploits does not imply safety. Apply the recommended fix and use O3 Security to monitor your exposure.

What is the EPSS score for CVE-2026-47077?

CVE-2026-47077 has an EPSS (Exploit Prediction Scoring System) score of 0.7%, placing it in the 53th percentile of all CVEs. EPSS is maintained by FIRST.org and estimates the probability that a vulnerability will be exploited in the wild within the next 30 days. This score indicates relatively lower exploitation probability, though the CVSS severity should still guide your patching priority.

What type of vulnerability is CVE-2026-47077?

CVE-2026-47077 is classified as Uncontrolled Resource Consumption (CWE-400). This weakness type describe the underlying flaw category, which helps determine the potential impact and the right class of mitigation.

When was CVE-2026-47077 published, and has it been updated?

CVE-2026-47077 was published on May 25, 2026 and was last updated on October 21, 2026. Advisory data evolves as severity scores, affected ranges, and exploit intelligence are revised — always check the latest version of the advisory before acting.

💧 Hex

Not in CISA KEV

CVE-2026-47077 — hackney

Fix: benoitc/hackney@3d25f9f

CVE-2026-47077 is a Uncontrolled Resource Consumption vulnerability in hackney. A fix is available for hackney — see the affected versions and patch details below.

Unbounded body accumulation in HTTP/3 response loop in hackney

Also known asEEF-CVE-2026-47077GHSA-jq4m-q6p2-8gwc

Published

May 25, 2026

Updated

Oct 21, 2026

Affected

1 pkg

Patched

1 / 1

Exploits

None indexed

Exploitation data as of Oct 24, 2026 · OSV.dev, NVD, FIRST.org (EPSS)

Exploitation Status

Proof-of-concept exploit code exists

CISA’s SSVC triage found public proof-of-concept exploit code for this CVE, though no confirmed active exploitation.
CISA assesses this as automatable — exploitation doesn’t require manual, per-target effort, which raises the odds of mass scanning and opportunistic attacks.

Exploitation and automatability from CISA’s SSVC triage for CVE-2026-47077.

EPSS Exploitation Probability

via FIRST.org ↗

0.7%probability of exploitation in next 30 days

Lower Risk0.00%

Lower risk than most CVEs53th percentile — riskier than 53% of all scored CVEsHighest risk

Probability of exploitation in the next 30 days, from FIRST.org EPSS.

Real-World Exposure

1 pkg affected

💧hackney

Real-time download stats are indexed for npm and PyPI packages. This vulnerability affects Hex packages — download data is not available via public APIs for these ecosystems.

Description

Summary

hackney_h3:await_response_loop/6 in src/hackney_h3.erl accumulates the HTTP/3 response body in memory without any size cap. The after Timeout clause is a per-message inactivity timer, not a wall-clock deadline: every received stream_data chunk, housekeeping select message, or settings frame resets it. A malicious HTTP/3 server that drips one small chunk every Timeout - 1 ms with Fin = false and never terminates the stream keeps the loop alive indefinitely while the accumulation buffer grows without bound, eventually exhausting the BEAM process heap.

Details

In src/hackney_h3.erl, await_response_loop/6 (line 430) builds the body with:

NewBody = <<AccBody/binary, Data/binary>>

There is no max_body check and no monotonic deadline. The after Timeout clause at line 463 is restarted on each loop iteration. A server that ensures at least one message arrives within Timeout ms indefinitely (one small chunk per interval is sufficient) prevents the timeout from firing while AccBody grows linearly. The same module's wait_connected/3 (lines 388-389) shows the correct pattern: track an absolute start time and pass a shrinking Remaining budget into each receive. This loop does not.

Configurations

Only the HTTP/3 transport is affected. Applications using the default TCP/TLS hackney transport are not vulnerable. The vulnerability requires using hackney_h3 directly or passing {transport, h3} to hackney:request/5.

PoC

Stand up an HTTP/3 server that responds with 200 OK headers (Fin = false), then emits a small stream_data chunk every Timeout - margin ms with Fin = false indefinitely.
Issue hackney:request(get, Url, [], <<>>, [{transport, h3}]) against it.
Watch the client process heap grow monotonically. The configured timeout never fires; the process is eventually killed by max_heap_size or the OS OOM killer.

Impact

Remote denial of service via unbounded memory consumption. Affects hackney 2.0.0 through 4.0.0 when using the HTTP/3 transport against an attacker-controlled or attacker-influenced server. Each affected request consumes unbounded memory until the BEAM is killed. CVSS v4.0: 8.2 (HIGH).

Resources

Introduction commit: https://github.com/benoitc/hackney/commit/0334af206d5099fdf510ed9eda18e34396f065ad
Patch commit: https://github.com/benoitc/hackney/commit/3d25f9fea26c90609de9d64366fedfe5065413bc

Affected Packages

1 total 1 fixed

Ecosystem	Package	Vulnerable range	Fix
💧Hex	`hackney`	≥ 2.0.0&&< 4.0.1	4.0.1`mix deps.update hackney`

Affected Products

1 product · 1 configurations

Application

hackneybenoitc

≥ 2.0.0 && < 4.0.1

range

Detection & mitigation playbook

Open-source dependency

Detect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for hackney, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update hackney to 4.0.1 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-47077 is resolved across your whole dependency graph.
Workarounds
Cap what an attacker can consume: apply request size, rate and timeout limits in front of the affected component, and run it with memory and CPU limits so exhaustion degrades one worker rather than the whole service.

Frequently Asked Questions

### Summary `hackney_h3:await_response_loop/6` in `src/hackney_h3.erl` accumulates the HTTP/3 response body in memory without any size cap. The `after Timeout` clause is a per-message inactivity timer, not a wall-clock deadline: every received `stream_data` chunk, housekeeping `select` message, or `settings` frame resets it. A malicious HTTP/3 server that drips one small chunk every `Timeout - 1` ms with `Fin = false` and never terminates the stream keeps the loop alive indefinitely while the accumulation buffer grows without bound, eventually exhausting the BEAM process heap. ### Details I

O3 Security · Impact-Aware SCA

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