High [CVE-2026-63984] fix hdrlen overflow in ipv6_rpl_srh_decompress
This high-severity Red Hat Linux advisory covers CVE-2026-63984 affecting Red Hat Enterprise Linux 10, Red Hat Enterprise Linux 6, Red Hat Enterprise Linux 9.
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Summary
In the Linux kernel, the following vulnerability has been resolved: ipv6: rpl: fix hdrlen overflow in ipv6_rpl_srh_decompress() ipv6_rpl_srh_decompress() computes: outhdr->hdrlen = (((n + 1) * sizeof(struct in6_addr)) >> 3); hdrlen is __u8. For n >= 127 the result exceeds 255 and silently truncates.
With n=127 (cmpri=15, cmpre=15, pad=0, hdrlen=16): (128 * 16) >> 3 = 256, truncated to 0 as __u8 The caller in ipv6_rpl_srh_rcv() then places the compressed header at buf + ((ohdr->hdrlen + 1) 255, which prevents n+1 from overflowing unsigned char (the segments_left field), but does not prevent the computed hdrlen from overflowing __u8. n=127 passes because 128 127.
This caps n at 126, giving hdrlen = (127 * 16) >> 3 = 254, which fits in __u8. The compressed header then lands at buf + ((254 + 1) << 3) = buf + 2040, exactly past the decompressed region (buf[0..2039]).
127 segments is well beyond any realistic RPL deployment. A flaw was found in the Linux kernel's IPv6 Routing Protocol for Low-Power and Lossy Networks (RPL) segment routing header (SRH) decompression function, ipv6_rpl_srh_decompress().
An integer overflow occurs when processing a specially crafted IPv6 packet, causing the header length calculation to truncate. This vulnerability could allow a remote attacker to cause data corruption.
Affected versions
No affected-version range was extracted from the source record. The vendor advisory is authoritative — check it before change work.
Official advisory · medium-confidence parse· fetched 6 days ago·verify at source
Fixed versions
No fixed release is recorded yet. That does not prove no patch exists — confirm against the vendor advisory.
Official advisory · medium-confidence parse· fetched 6 days ago·verify at source
Mitigation
The source record does not include mitigation steps. That is not a statement that no fix exists — read the vendor advisory below for the authoritative guidance.
Official advisory · medium-confidence parse· fetched 6 days ago·verify at source
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