CVE-2021-36769Network attack vector

Message-order manipulation via unchecked MTProto sequence metadata

Published Jul 16, 2021 · Updated Aug 4, 2024

Message reordering in Telegram for Android before 7.8.1, iOS before 7.8.3, and Desktop before 2.8.8 allows attackers to alter delivery order. The server accepts a lower msg_id when its msg_seq_no is also lower and checks the embedded timestamp only against a broad validity window, so delayed ciphertexts are processed out of order. A man-in-the-middle attacker must control network delivery and can reorder only outgoing, undelivered messages without learning their contents.

CVSS severity5.3
Medium
EPSS probability1.39%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Message reordering in Telegram for Android before 7.8.1, iOS before 7.8.3, and Desktop before 2.8.8 allows attackers to alter delivery order. The server accepts a lower msg_id when its msg_seq_no is also lower and checks the embedded timestamp only against a broad validity window, so delayed ciphertexts are processed out of order. A man-in-the-middle attacker must control network delivery and can reorder only outgoing, undelivered messages without learning their contents.

The record

CVE
CVE-2021-36769
Published
Jul 16, 2021
Updated
Aug 4, 2024
Vendor
Unknown vendor
Product
Unknown product
Classifications
CWE-326, T1565.002
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Jul 16, 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

5.3UbuntuCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N

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.

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No observations available

Sep 9, 2026Sep 15, 2026
Latest reporting daySep 15, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-326Inadequate Encryption Strength
T1565.002Transmitted Data Manipulation

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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