NVD / CVE Program· CNA GitHub_M

CVE-2025-43857: net-imap rubygem vulnerable to possible DoS by memory exhaustion

Noroxi assessment

Priority: Monitor (action score 24/100)

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: 0.49% (FIRST EPSS).
Anyone who can reach it over the internet can trigger it. No account or password is required. No special conditions are required; it is repeatable.
Fixed version: ruby-net-imap (Alpine:v3.20) 0.4.22-r0; net-imap (RubyGems) 0.3.9, 0.4.20, 0.5.7.

Low priority for now. Upgrade to ruby-net-imap (Alpine:v3.20) 0.4.22-r0; net-imap (RubyGems) 0.3.9, 0.4.20, 0.5.7 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

Net::IMAP implements Internet Message Access Protocol (IMAP) client functionality in Ruby. Prior to versions 0.5.7, 0.4.20, 0.3.9, and 0.2.5, there is a possibility for denial of service by memory exhaustion when net-imap reads server responses. At any time while the client is connected, a malicious server can send can send a "literal" byte count, which is automatically read by the client's receiver thread. The response reader immediately allocates memory for the number of bytes indicated by the server response. This should not be an issue when securely connecting to trusted IMAP servers that are well-behaved. It can affect insecure connections and buggy, untrusted, or compromised servers (for example, connecting to a user supplied hostname). This issue has been patched in versions 0.5.7, 0.4.20, 0.3.9, and 0.2.5.

MediumCVSS 6.0 · v4.0—No exploit Fix available

Published: Apr 28, 2025
Updated: Jun 17, 2026
EPSS: 0.4% · 42th percentile
CWE: CWE-400

Report tools

JSON

Action score

Monitor

Low priority for now.

CVSS: 24 / 40 · 6.0 / 10
CISA KEV: 0 / 30 · Not listed
EPSS: 0 / 30 · 0.4%

CISA SSVC decision

Exploitation: none
Automatable: no
Technical impact: partial

Vulnrichment: CISA's decision-tree inputs.

CNA vs NVD score

NVD: —
CNA · GitHub_M: 6.0; NVD has not scored this yet; the score shown is the CNA’s.

CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:P/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
ruby-lang	net\	cpe:2.3:a:ruby-lang:net\

Affected versions

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

ruby-lang net::imapbefore 0.2.5
ruby-lang net::imap0.3.0 and later · before 0.3.9
ruby-lang net::imap0.4.0 and later · before 0.4.20
ruby-lang net::imap0.5.0 and later · before 0.5.7

Versions reported by the vendor

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

ruby net-imap
- >= 0.5.0, < 0.5.7, >= 0.4.0, < 0.4.20, >= 0.3.0, < 0.3.9, >= 0, < 0.2.5affected

Package-level exposure

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

Ecosystem	Package	Affected range	Fix
Alpine:v3.20	ruby-net-imap	before 0.4.22-r0	0.4.22-r0
Debian:12	ruby3.1	from 0	—
Debian:13	ruby3.3	from 0	—
RubyGems	net-imap	from 0.3.0 · before 0.3.9	0.3.9
RubyGems	net-imap	from 0.4.0 · before 0.4.20	0.4.20
RubyGems	net-imap	from 0.5.0 · before 0.5.7	0.5.7
RubyGems	net-imap	before 0.2.5	0.2.5

Same product

ruby-lang: all records

Other highest-scoring records for the same primary product.

CVE-2026-42246net-imap vulnerable to STARTTLS stripping via invalid response timing
30Monitor
CVE-2026-42256net-imap: Denial of service via high iteration count for `SCRAM-*` authentication
24Monitor
CVE-2026-42258net-imap: Command Injection via unvalidated Symbol inputs
23Monitor

Published before and after this one in the same product

Later →CVE-2026-42245May 9, 2026 · net-imap: Quadratic complexity when reading response literals
9Monitor
Later →CVE-2026-42257May 9, 2026 · net-imap: Command Injection via "raw" arguments to multiple commands
23Monitor

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
alpine:ruby-net-imap	0.4.22-r0 · Alpine:v3.20	Package registry (OSV)
RubyGems:net-imap	0.2.5	Package registry (OSV)
RubyGems:net-imap	0.3.9	Package registry (OSV)
RubyGems:net-imap	0.4.20	Package registry (OSV)
RubyGems:net-imap	0.5.7	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.

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.

No credits in the CNA record.

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

RubyHackerOne · paid

The product’s vendor appears in a public program. Matched by name; verify the scope text in the program.

Technical details

Attack conditions

Anyone who can reach it over the internet can trigger it.
No account or password 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: P
Scope: X

Weakness class (CWE)

CWE-400 · Uncontrolled Resource Consumption

CVSS vector

CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:P/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, 10:46 PM UTC

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References

github.com/ruby/net-imap/pull/442

Show all references (5 more)

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

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