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CVE-2026-71884— Packet CTR reports a full success length after the counter is exhausted

Quick assessment

Affected
Legion of the Bouncy Castle Inc. BC-LTS-JAVA
Exploitation
No confirmed in-the-wild exploitation; assess based on exposure
Recommended action
Check the vendor advisory and references for a fixed version. If immediate upgrade is impossible, restrict exposure and increase monitoring.

以下是该漏洞描述信息的中文翻译： 在 Java 长期支持版（LTS）的 Bouncy Castle 2.73.13 版本之前，原生的单次（one-shot）CTR 分组密码未检查所请求的输入长度是否超出 IV（初始化向量）所允许的计数器范围。 在 CTR 模式下，IV 和分组计数器共享同一个 16 字节的块。因此，当 IV 长度为 13 至 15 字节时，剩余的计数器长度仅为 1 至 3 字节，分别只能寻址 256、65536 或 16777216 个分组。如果输入数据过长，计数器会发生回绕（wrap），导致密钥流

CVSS 8.2 · High

Possible ATT&CK Techniques 1 AI

T1190 · Exploit Public-Facing Application

Affected Version Matrix 1

VendorProduct Version RangeStatus
Legion of the Bouncy Castle Inc. BC-LTS-JAVA 2.73.4< 2.73.13 affected
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I. Basic Information for CVE-2026-71884

Vulnerability Information
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Vulnerability Title
Packet CTR reports a full success length after the counter is exhausted
Source: CVE Program / CVE List V5
Vulnerability Description
In Bouncy Castle for Java LTS before 2.73.13, the native one-shot CTR packet cipher did not check that the requested input length fitted the counter space the IV left. In CTR mode the IV and the block counter share one 16-byte block, so an IV of 13 to 15 bytes leaves a counter of only 1 to 3 bytes, addressing 256, 65536 or 16777216 blocks respectively. Given a longer input the counter wrapped and the keystream repeated from the start of the same packet, and the call then returned the full input length as though every byte had been correctly transformed. Two segments of the message were therefore encrypted under the same keystream, so their plaintexts can be recovered from the ciphertext alone, without the key, while the caller saw neither an exception nor a short length to indicate it. The streaming implementation validates at init and again while processing, and the portable AESCTRPacketCipher rejects such a request with "Counter in CTR/SIC mode out of range.", but the native one-shot path has a single entry point and performed no counter-range validation there. It now preflights the IV-derived counter range and rejects an over-long request before any output is written, so the operation is failure-atomic and never reports success for bytes it did not correctly transform. A counter of four bytes or more cannot be exhausted by a Java int length and is unaffected, as is a full 16-byte IV, where the counter range is the caller's responsibility. Bouncy Castle for Java (bcprov) is not affected, as it ships no native implementations.
Source: CVE Program / CVE List V5
CVSS Information
CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:H/VI:N/VA:N/SC:N/SI:N/SA:N/U:Amber
Source: CVE Program / CVE List V5
Vulnerability Type
在加密中重用Nonce与密钥对
Source: CVE Program / CVE List V5

Affected Products

Vendor Product Affected Versions CPE Subscribe
Legion of the Bouncy Castle Inc. BC-LTS-JAVA 2.73.4 ~ 2.73.13 -

II. Public POCs for CVE-2026-71884

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III. Intelligence Information for CVE-2026-71884

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Proof of Concept for CVE-2026-71884 (1)

IV. Related Vulnerabilities

Same product: BC-LTS-JAVA
Same vendor: Legion of the Bouncy Castle Inc.
Same weakness: CWE-323

V. Comments for CVE-2026-71884

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