CVE-2020-27539Network attack vector

Memory corruption via mismatched HTTP body copy

Published Jan 25, 2021 · Updated Aug 4, 2024

Heap-buffer overflow in AgentUpdater in Rostelecom CS-C2SHW 5.0.082.1 allows attackers to corrupt memory via a crafted HTTP response. The parser allocates pld_buf from Content-Length plus one, then copies body bytes using a length derived from the complete response buffer and body offset, causing an out-of-bounds write. Default configuration fully parses only responses from vendor-set HTTPS URLs, so exploitation requires another flaw or configuration change; code execution is discussed but not demonstrated.

CVSS severity9.8
Critical
EPSS probability1.26%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Heap-buffer overflow in AgentUpdater in Rostelecom CS-C2SHW 5.0.082.1 allows attackers to corrupt memory via a crafted HTTP response. The parser allocates pld_buf from Content-Length plus one, then copies body bytes using a length derived from the complete response buffer and body offset, causing an out-of-bounds write. Default configuration fully parses only responses from vendor-set HTTPS URLs, so exploitation requires another flaw or configuration change; code execution is discussed but not demonstrated.

The record

CVE
CVE-2020-27539
Published
Jan 25, 2021
Updated
Aug 4, 2024
Vendor
Unknown vendor
Product
Unknown product
Classifications
CWE-787, T1203
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Jan 25, 2021CVE publishedPublication date reported by the CVE source.
  2. Aug 4, 2024Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Affected buildAffected product and version details are unavailable.

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Affected products and versions are unavailable in this record.

Published CVSS scores

9.8NIST NVDCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
7.5NIST NVDAV:N/AC:L/Au:N/C:P/I:P/A:P

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-787Out-of-bounds Write
T1203Exploitation for Client Execution

Public exploit references

No public exploit references are available in this record.

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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