CVE-2021-31320Public exploitNetwork attack vector

Client memory corruption via unbounded gradient index

Published May 18, 2021 · Updated Aug 3, 2024

Heap overflow in Telegram Android before 7.1.0 (2090), iOS before 7.1, and macOS before 7.1 allows remote attackers to corrupt memory. The VGradientCache::generateGradientColorTable loop fails to bound pos against the 1,024-entry colorTable while a sticker-controlled gradient stop advances the index, causing four-byte writes beyond the heap buffer. Exploitation requires delivery through a secret chat and the victim to open that chat; the demonstrated consequence is a persistent client crash with attacker-influenced heap corruption.

CVSS severity7.1
High
EPSS probability1.22%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Heap overflow in Telegram Android before 7.1.0 (2090), iOS before 7.1, and macOS before 7.1 allows remote attackers to corrupt memory. The VGradientCache::generateGradientColorTable loop fails to bound pos against the 1,024-entry colorTable while a sticker-controlled gradient stop advances the index, causing four-byte writes beyond the heap buffer. Exploitation requires delivery through a secret chat and the victim to open that chat; the demonstrated consequence is a persistent client crash with attacker-influenced heap corruption.

The record

CVE
CVE-2021-31320
Published
May 18, 2021
Updated
Aug 3, 2024
Vendor
Unknown vendor
Product
Unknown product
Classifications
CWE-787, T1203
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. May 18, 2021CVE publishedPublication date reported by the CVE source.
  2. Aug 3, 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

5.8NVDAV:N/AC:M/Au:N/C:N/I:P/A:P
7.1NVDCVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:N/I:H/A:H

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 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 exploitPublished

Weakness, pattern, technique

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

Public exploit references

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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