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NVD / CVE Program· CNA EEF

CVE-2026-39803: HTTP/1 chunked body reader ignores length cap in bandit

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: 0.64% (FIRST EPSS); higher than 51% 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: mtrudel bandit 1.11.1, ae3520dfdbfab115c638f8c7f6f6b805db34e1ab.

Low priority for now. Upgrade to mtrudel bandit 1.11.1, ae3520dfdbfab115c638f8c7f6f6b805db34e1ab 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

Allocation of Resources Without Limits or Throttling vulnerability in mtrudel bandit allows unauthenticated remote denial of service via memory exhaustion. The chunked clause of 'Elixir.Bandit.HTTP1.Socket':read_data/2 in lib/bandit/http1/socket.ex ignores the caller-supplied :length option when reading HTTP/1 chunked request bodies. Instead of capping the accumulated body at the configured limit (e.g. Plug.Parsers' default 8 MB), do_read_chunked_data!/5 buffers every received chunk into an iolist unconditionally and materializes the entire body as a single binary. The function always returns {:ok, body, ...}, so callers cannot interpose a 413 response. Because Plug.Parsers runs before routing and authentication in the standard Phoenix endpoint, an unauthenticated attacker needs no valid route or credentials. Sending a single Transfer-Encoding: chunked POST request with an arbitrarily large body to any path causes the BEAM process to exhaust available memory and be terminated by the OS OOM killer. The content-length path in the same function correctly enforces the limit and is not affected. This issue affects bandit: from 1.4.0 before 1.11.1.

HighCVSS 8.7 · v4.0—No exploit Fix available
Published
May 13, 2026
Updated
Oct 26, 2026
EPSS
0.6% · 51th 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 · 0.6%

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-2026-39803

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
mtrudelbandit

Affected versions

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

  • mtrudel bandit1.4.0 and later · before 1.11.1

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.

  • mtrudel bandit

    • 1.4.0 and later · before 1.11.1affected · semver
    • 903e209a521bc216b9f9065c01ae9a0cac2d5a10 and later · before ae3520dfdbfab115c638f8c7f6f6b805db34e1abaffected · git

Package-level exposure

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

EcosystemPackageAffected rangeFix
Hexbanditfrom 1.4.0 · before 1.11.11.11.1

Same product

mtrudel: all records

Other highest-scoring records for the same primary product.

  • CVE-2026-116078HTTP/2 request bodies made of 1-byte DATA frames amplify memory use in Bandit
    34Monitor
  • CVE-2026-115269HTTP/2 WINDOW_UPDATE and SETTINGS frames reset the request body read timeout in Bandit
    34Monitor
  • CVE-2026-114213WebSocket 1-byte continuation frames bypass `max_fragmented_message_size` in Bandit
    34Monitor

Published before and after this one in the same product

  • ← EarlierCVE-2026-42786May 1, 2026 · WebSocket fragmented message reassembly unbounded in bandit
    34Monitor
  • ← EarlierCVE-2026-42788May 1, 2026 · HTTP/2 frame size limit checked after body is buffered in bandit
    27Monitor
  • Later →CVE-2026-39806May 13, 2026 · HTTP/1 chunked decoder infinite loop on requests with trailer fields in bandit
    34Monitor

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
mtrudel bandit1.11.1Vendor (CNA)
mtrudel banditae3520dfdbfab115c638f8c7f6f6b805db34e1abVendor (CNA)
Hex:bandit1.11.1Package 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.

  • CVE-2026-4278612 days apartWebSocket fragmented message reassembly unbounded in bandit
    34Monitor
  • CVE-2026-7483699 days apartHTTP/2 connection-window starvation pins Plug processes indefinitely in Bandit
    34Monitor
  • CVE-2026-108525166 days apartHTTP/2 inbound flow control is not enforced, letting a client queue unbounded DATA in stream processes in Bandit
    34Monitor
  • CVE-2026-111101166 days apartHTTP/1.1 chunked request bodies made of 1-byte chunks amplify memory use in Bandit
    34Monitor
  • CVE-2026-114213166 days apartWebSocket 1-byte continuation frames bypass `max_fragmented_message_size` in Bandit
    34Monitor
  • CVE-2026-115269166 days apartHTTP/2 WINDOW_UPDATE and SETTINGS frames reset the request body read timeout in Bandit
    34Monitor

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-770 · Allocation of Resources Without Limits or Throttling

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.

Change log

  1. Fix✗ → ✓

For records you follow, these changes also arrive as notifications. →

References

Show all references (2 more)

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

All records