NVD / CVE Program· CNA EEF

CVE-2026-7790: Unbounded chunk-size hex digits in cowlib cause quadratic CPU and memory DoS

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: 0.43% (FIRST EPSS).
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: ninenines cowlib 2.16.1, a4b8039ce8c93ab00867ef6b7e888822c09f4369; azl3 rabbitmq-server 3.13.7-3 on Azure Linux 3.0 3.13.7-4; azl3 rabbitmq-server 3.13.7-5 on Azure Linux 3.0 3.13.7-5.

Low priority for now. Upgrade to ninenines cowlib 2.16.1, a4b8039ce8c93ab00867ef6b7e888822c09f4369; azl3 rabbitmq-server 3.13.7-3 on Azure Linux 3.0 3.13.7-4; azl3 rabbitmq-server 3.13.7-5 on Azure Linux 3.0 3.13.7-5 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

Uncontrolled Resource Consumption vulnerability in ninenines cowlib (cow_http_te module) allows Excessive Allocation. The chunked transfer-encoding parser in cow_http_te accepts an unbounded number of hex digits in the chunk-size field. Each digit causes a bignum multiplication (Len * 16 + digit), so parsing N hex digits requires O(N²) CPU work and O(N) memory. Additionally, when input is drip-fed, the parser discards the accumulated length on each partial read and restarts from zero on resumption, raising the cost to O(N³). An unauthenticated remote attacker can exploit this by sending an HTTP/1.1 request with Transfer-Encoding: chunked and a very long chunk-size hex string to cause denial of service through CPU exhaustion and memory amplification. This vulnerability is associated with program file src/cow_http_te.erl and program routines cow_http_te:stream_chunked/2, cow_http_te:chunked_len/4. This issue affects cowlib: from 0.6.0 before 2.16.1.

HighCVSS 8.7 · v4.0—No exploit Fix available

Published: May 11, 2026
Updated: Oct 26, 2026
EPSS: 0.4% · 37th percentile
CWE: CWE-400

Report tools

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Action score

Monitor

Low priority for now.

CVSS: 34 / 40 · 8.7 / 10
CISA KEV: 0 / 30 · Not listed
EPSS: 0 / 30 · 0.4%

CISA SSVC decision

Exploitation: none
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

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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.

Vendor	Product	CPE
ninenines	cowlib	cpe:2.3:a:ninenines:cowlib

Affected versions

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

ninenines cowlib0.6.0 and later · before 2.16.1

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.

ninenines cowlib
- 0.6.0 and later · before 2.16.1affected · semver
- 8c0e428b012c59f553a264f285ed89d36f791e3e and later · before a4b8039ce8c93ab00867ef6b7e888822c09f4369affected · git

Package-level exposure

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

Ecosystem	Package	Affected range	Fix
Debian:12	erlang-cowlib	from 0	—
Debian:14	erlang-cowlib	before 2.17.1-1	2.17.1-1
Hex	cowlib	from 0.6.0 · before 2.16.1	2.16.1

Same product

ninenines: all records

Other highest-scoring records for the same primary product.

CVE-2026-59248Unbounded HPACK/QPACK prefixed-integer decoding in Cowlib causes memory-exhaustion DoS
34Monitor
CVE-2026-43970Decompression Bomb in cow_spdy:inflate/2 Allows Memory Exhaustion via Crafted SPDY Frame
32Monitor
CVE-2026-43971Link Header Directive Smuggling via Unescaped target/rel/Attribute Keys in cow_link:link/1
25Monitor

Published before and after this one in the same product

← EarlierCVE-2026-43968May 11, 2026 · CR Injection in SSE Encoder Enables Event Splitting via cow_sse:event/1
25Monitor
← EarlierCVE-2026-43969May 11, 2026 · Cookie Request Header Injection via Unvalidated Encoder in cow_cookie:cookie/1
8Monitor
Later →CVE-2026-43966Jun 8, 2026 · HTTP Response Splitting via Non-VCHAR Bytes in cow_http_struct_hd:escape_string/2
25Monitor

Remediation

Which version to upgrade to

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

Product / package	Fixed version	Source
ninenines cowlib	2.16.1	Vendor (CNA)
ninenines cowlib	a4b8039ce8c93ab00867ef6b7e888822c09f4369	Vendor (CNA)
azl3 rabbitmq-server 3.13.7-3 on Azure Linux 3.0	3.13.7-4 · CBL-Mariner Releases	Microsoft (MSRC)
azl3 rabbitmq-server 3.13.7-5 on Azure Linux 3.0	3.13.7-5 · CBL-Mariner Releases	Microsoft (MSRC)
debian:erlang-cowlib	2.17.1-1 · Debian:14	Package registry (OSV)
Hex:cowlib	2.16.1	Package 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.

EPSS, last 120 days

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.

ninenines/cowlibcommit a4b8039

Credits

All researchers

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

Peter Ullrichfinder
Loïc Hoguinremediation developer

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-400 · Uncontrolled Resource Consumption

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

Root cause

Code that parses nested structures sets no depth or size limit. A small input can turn into a disproportionate processing load.

The bug in code

The whole CWE-400 class

A representative example of this vulnerability class. Not the vendor's source code; it shows the faulty pattern and its fix.

Vulnerable

1function expand(node) {
2  return node.children.map(expand);
3}

Fixed

1const MAX_DEPTH = 32;
2function expand(node, depth = 0) {
3  if (depth > MAX_DEPTH) throw new Error("too deep");
4  return node.children.map((c) => expand(c, depth + 1));
5}

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

Endpoint Denial of ServiceT1499

Change log

Fix✗ → ✓Sep 28, 2026, 10:07 PM UTC

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References

cna.erlef.org/cves/CVE-2026-7790.html

Show all references (2 more)

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

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